dnl # The following example makes mail from this host and any additional
dnl # specified domains appear to be sent from mydomain.com
dnl #
dnl MASQUERADE_AS(`mydomain.com')dnl
dnl #
dnl # masquerade not just the headers, but the envelope as well
dnl #
dnl FEATURE(masquerade_envelope)dnl
dnl #
dnl # masquerade not just @mydomainalias.com, but @*.mydomainalias.com as well
dnl #
dnl FEATURE(masquerade_entire_domain)dnl
dnl #
dnl MASQUERADE_DOMAIN(localhost)dnl
dnl MASQUERADE_DOMAIN(localhost.localdomain)dnl
dnl MASQUERADE_DOMAIN(mydomainalias.com)dnl
dnl MASQUERADE_DOMAIN(mydomain.lan)dnl
MAILER(smtp)dnl
MAILER(procmail)dnl
dnl MAILER(cyrusv2)dnl
MASQUERADE_DOMAIN(`verizon.net')dnl
MASQUERADE_AS(`moonpoint.com')dnl

After I edited the sendmail.mc file, I rebuilt the sendmail.cf file by restarting sendmail with the command service sendmail restart , which put the following line in sendmail.cf:

C{M}verizon.net

The person who was sending the newsletter died several years ago and I took over maintaining the membership list for the organization as well as distributing the email version of the newsletters to members. Though the account from which the newsletter is sent is intended to be used only for sending the newsletter and members are advised to send an email related to the organization to the organization's Gmail email addresses, occasionally members will reply directly to the "from" address used for the newsletter. When checking the account for that address, I found that someone with a verizon.net address had sent a reply to the account, but if I replied my reply would go not to his verizon.net address, but to his email name followed by my domain name, which would result in the email bouncing since that address would not be a valid address on my server. I corrected the problem by removing the two MASQUERADE lines in sendmail.mc that resulted in the change to the domain name part of email addresses if any email came from a verizon.net address and then restarted sendmail, which resulted in the C{M}verizon.net line being removed from sendmail.cf.

The sendmail.mc file is a human-readable macro configuration file, while the sendmail.cf file is the more complex configuration file actually used by the Sendmail message transfer agent (MTA). The .mc file serves as the source, which is processed by the m4 macro to generate the final, often uncommented sendmail.cf file used by sendmail. The command m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf can be used to rebuild the .cf configuration file after one makes changes to the sendmail.mc file, but the changes won't take effect until sendmail is restarted. Or, on many newer versions of the Linux operating system, one can simply restart sendmail and a new .cf file will be automatically generated and applied to sendmail, if any changes have been made to the .mc file

References:

1. 18.4. The sendmail.cf and sendmail.mc Files
   Linux Network Administrators Guide

Related articles:

1. Modifying the "from" domain of a message with sendmail
   Date: June 1, 2018

[/network/email/sendmail] permanent link

To change the "from" address of a message in the Mutt email client while composing a message, you can use Esc-f, i.e., hit the Esc and f keys simultaneously. You will see a "From:" field appear near the bottom of the window with the current "from" address, which you can edit to replace it with whatever you would like. E.g., in the example below, I am changing the "from" address that the recipients of the message will see from jdoe@example.com to newsletter@example.com (the email address is within the angle brackets with a descriptive identifier before it.

y:Send q:Abort t:To c:CC s:Subj a:Attach file d:Descrip ?:Help               
    From: Joe Doe <jdoe@example.com>
      To: "Bruce K." <bkamen2145@gmail.com>
      Cc: albusd@example.com
     Bcc:
 Subject: Re: July 2025 Newsletter
Reply-To:
     Fcc: ~/sent
Security: None


-- Attachments                                                               
- I 1 /var/tmp/mutt-example-508-23668-418711[text/plain, 8bit, utf-8, 1.4K   




-- Mutt: Compose [Approx. msg size: 1.4K Atts: 1]----------------------------
From: Newsletter <newsletter@example.com>

After I've retyped the "from" address to be the one I want to appear, when I hit Enter, I will see the "from" address replaced with the one I want and can then hit y to send the message to recipients.

y:Send q:Abort t:To c:CC s:Subj a:Attach file d:Descrip ?:Help               
    From: Newsletter <newsletter@example.com>
      To: "Bruce K." <bkamen2145@gmail.com>
      Cc: albusd@example.com
     Bcc:
 Subject: Re: July 2025 Newsletter
Reply-To:
     Fcc: ~/sent
Security: None


-- Attachments                                                               
- I 1 /var/tmp/mutt-example-508-23668-418711[text/plain, 8bit, utf-8, 1.4K   




-- Mutt: Compose [Approx. msg size: 1.4K Atts: 1]----------------------------

For a way to change the "from" address from the command line, see Using a command-line interface (CLI) to send email with mutt.

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• Apple
• Google (online)
• Office 365 (onlilne)
• Outlook
• Outlook.com
• Yahoo (online)

Once I had the .ics file, I was able to click on File then Open & Export in Outlook on my wife's PC to open the .ics file I downloaded and add the organization's calendar to her Outlook calendar.

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For a mail server running Sendmail email server software, if you wish to block email from a particular "from" address to any email address on the server, you can include the address you wish to block in the /etc/mail/access file. E.g., if you wished to block email from the address spammer@example.com, you can include the following line in that file:

# Block envelope "from" address of spammers
spammer@example.com                     REJECT

Any line beginning with a # is treated as a comment, so the first line above isn't needed, but adding a comment line may help you recognize why the reject statement is in the file. After you have added the line, you need to regenerate the /etc/mail/access.db file, or create a new one if there isn't already one present, using the command shown below (you don't need to restart sendmail):

# makemap hash /etc/mail/access </etc/mail/access
#

This will only work if you have a FEATURE(`access_db')dnl line in /etc/mail/sendmail.mc. E.g., a line like the one below:

FEATURE(`access_db', `hash -T<TMPF> -o /etc/mail/access.db')dnl

If you don't have such a line, you will need to add it. If the line begins with dnl, you will need to remove the dnl at the beginning of the line, since that "comments out" the line.

[ More Info ]

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SSLCertificateFile /etc/letsencrypt/live/support.moonpoint.com-0001/cert.pem
SSLCertificateKeyFile /etc/letsencrypt/live/support.moonpoint.com-0001/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
SSLCertificateChainFile /etc/letsencrypt/live/support.moonpoint.com-0001/chain.pem

When I checked the expiration of that security certificate, I saw it was valid until May 17.

# openssl x509 -enddate -noout -in /etc/letsencrypt/live/support.moonpoint.com-0001/cert.pem
notAfter=May 17 04:02:51 2024 GMT
#

You can determine the location of the .pem file used by Dovecot by looking for the ssl_cert variable in /etc/dovecot/conf.d/10-ssl.conf.

[ More Info ]

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A family member reported she was no longer able to send email via a Sendmail service I have running on a CentOS Linux system. She sent me a screenshot of the message she received when attempting to send a message. I saw a "Server error: '550 5.7.1 ... Relaying denied'" message. At first, I thought that a technician from her Internet Service Provider (ISP) might have changed her Microsoft Outlook settings when he upgraded her network equipment recently, but then I remembered I was restricting email relaying on the system by IP address and realized her IP address would have changed when the technician upgraded her network equipment. So I had her visit whatismyipaddress.com and provide me with the public IPv4 IP address it showed for her. I then replaced her prior IP address in /etc/mail/access. The format for an entry to allow relaying from a particular IP address is as shown below.

# Jane Doe
192.168.71.77                           RELAY

You can include a comment to indicate who the IP address is associated with by prefixing the comment with a pound sign. The IP address should be followed by the word "RELAY" (you can put tabs in between the IP address and the word, if you like).

After changing the IP address, I rebuilt the access database with the makemap command. I then restarted Sendmail

# makemap hash /etc/mail/access </etc/mail/access
# service sendmail restart
Redirecting to /bin/systemctl restart  sendmail.service
#

I was then able to receive a test message she sent me. After updating the IP address, I may only have needed to restart Sendmail without running the makemap command first as I found the following at 19.3.2. Sendmail on a Red Hat website in reference to running the make all -C /etc/mail/ command (CentOS is derived from Red Hat Enterprise Linux):

All other generated files in /etc/mail (db files) will be regenerated if needed. The old makemap commands are still usable. The make command is automatically used whenever you start or restart the sendmail service.

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1. Open Outlook and click on Next at the startup window.
2. When prompted as to whether you would like to configure an E-mail account, maintain the default option of "yes" and click on Next.
3. At the Add New Account window, choose "Manually configure server settings or additional server types" and then click on Next.
4. At the Choose Service window, maintain the default option of "Internet E-mail" and click on Next.
5. At the Internet E-mail Settings window, you will need to provide the relevant information for your AOL email account. In the username field, include "@aol.com" as part of the user name, e.g., jdoe@aol.com. You will also need to choose whether you will access your AOL email account using the Post Office Protocol (POP) or the Internet Message Access Protocol (IMAP). The default option is POP3, version 3 of POP. With that option, the email in your inbox will be downloaded to Outbox and deleted from the server after a specified period of time; by default Outlook will leave it on the server for 14 days. If you log into the AOL website to check your email after you've downloaded it with Outlook and delete a message while viewing your email in a browser, it won't be available to download with Outlook, if you subsequently check your AOL email with Outlook, although that may not matter to you. A disadvantage of using the POP protocol is that it only downloads email from the inbox, not any other folders you may have created to hold specific email messages. Also, by default email is deleted from the email server after you download it to Outlook, so email you've already downloaded won't be visible to you if you check your email through a web browser at a later time—by default Outlook will leave the email there for 14 days, though. You can change that setting, though, once you've filled in account information by clicking on the More Settings button, then clicking on the Advanced tab and choosing how long a copy of messages should be left on the server.

   If you select IMAP for the account type, you can view email in other folders besides the inbox and Outlook's view of the email in your account is synchronized with the email messages maintained on the AOL email server, so you can check with a web browser or with Outlook and see the same messages in your email folders. You could also set up Outlook on another system and select IMAP there as well to see the same email messages on a separate system where you are using Outlook.

   The information you should put in the incoming mail server and outgoing mail server fields is as follows:

   Protocol	Server	Port Settings
   POP3	Incoming mail server (POP3): pop.aol.com Outgoing mail server (SMTP): smtp.aol.com	POP3: 995-SSL SMTP: 465-SSL
   IMAP	Incoming mail server (IMAP): imap.aol.com Outgoing mail server (SMTP): smtp.aol.com	IMAP: 993-SSL SMTP: 465-SSL

   Put a check mark in the "Remember password" check box, if you don't want to have to enter your password every time you open Outlook to check your email.

[ More Info ]

[/network/email/AOL] permanent link

I use SparkPost to distribute a newsletter by email for an organization I support. A member of the organization reported to me that she has not been receiving email copies of the organization's newsletter, so I logged into the SparkPost account after this month's newsletter was sent and clicked on Events on the Dashboard, selected "Last 7 Days" in the Events Search date range selection field and then put the member's email address in the "Filter by recipient email address" field and hit Enter. I saw an "Injection" and a "Bounce" event whereas I would see an "Injection" and a "Delivery" event for email successfully sent to a recipient. When I clicked on the View Details button, I found that the email sent to the member bounced with SparkPost listing the reason as "554 5.7.1 [internal] recipient address was suppressed due to customer policy." At the SparkPost page on the problem, 554 5.7.1 — Recipient address was suppressed due to customer policy, I saw the possible reasons for that bounce message appear listed as those below:

1. The address was invalid (address does not exist)
2. The user clicked the list-unsubscribe header
3. The user clicked one of your emails and flagged it as SPAM. This FBL (FeedBack Loop) event should add that email address to your Suppression List.

[ More Info ]

[/network/email/sparkpost] permanent link

I needed to check on whether a system was functioning as a mail server listening on the Simple Mail Transfer Protocol Secure (SMTPS) port, TCP port 465. One way to check is to attempt to establish a telnet connection to that port. E.g.:

$ telnet 192.168.248.91 465
Trying 192.168.248.91...
Connected to esa.example.com
Escape character is '^]'.
^C
^CConnection closed by foreign host.
$

If you see a "connected to" message that indicates the system is listening on that port and you can terminate the connection by hitting Ctrl-C a couple of times. But you can also use an OpenSSL command as shown below to test SMTPS connectivity on TCP port 465:

$ openssl s_client -connect 192.168.248.91:465 -quiet
depth=0 /OU=Zimbra Collaboration Server/CN=esa.example.com
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 /OU=Zimbra Collaboration Server/CN=esa.example.com
verify error:num=27:certificate not trusted
verify return:1
depth=0 /OU=Zimbra Collaboration Server/CN=esa.example.com
verify error:num=21:unable to verify the first certificate
verify return:1
220 esa.example.com ESMTP Postfix
quit
221 2.0.0 Bye
$

If you leave the -quiet off the end of the command, you can see additional information about the certificate on the email server.

Related articles:

1. Using the openssl command to troubleshoot POP3S

[/network/email] permanent link