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Mon, May 22, 2023 10:05 pm

Relaying Denied by Sendmail

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 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                           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.

[/network/email/sendmail] permanent link

Fri, Jun 26, 2020 6:51 pm

Configuring Outlook 2010 to check AOL email

To configure Outlook 2010 to check an AOL email account, take the following steps.
  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 "" as part of the user name, e.g., 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:

    ProtocolServerPort Settings
    POP3Incoming mail server (POP3):
    Outgoing mail server (SMTP):
    POP3: 995-SSL
    SMTP: 465-SSL
    IMAPIncoming mail server (IMAP):
    Outgoing mail server (SMTP):
    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

Mon, Apr 20, 2020 10:45 pm

Removing an email address from a SparkPost suppression list

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

Fri, Oct 05, 2018 9:39 pm

Checking port 465 connectivity

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 465
Connected to
Escape character is '^]'.
^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 -quiet
depth=0 /OU=Zimbra Collaboration Server/
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 /OU=Zimbra Collaboration Server/
verify error:num=27:certificate not trusted
verify return:1
depth=0 /OU=Zimbra Collaboration Server/
verify error:num=21:unable to verify the first certificate
verify return:1
220 ESMTP Postfix
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

Fri, Jun 01, 2018 10:11 pm

Modifying the "from" domain of a message with sendmail

A user sends a monthly email newsletter to a distribution list on an email server I maintain that uses sendmail. He sends the message to an email alias on the system where sendmail converts the alias to all of the email addresses in the mailing list and the sends it out through a smart host to be delivered to all of the recipients of the newsletter. The sender sends the message from his address and I needed to convert the "from" address from a email address to a local email address on the server running sendmail. To do so, I placed the following lines at the end of /etc/mail/ For the example below, I use the domain as the local domain name for the server.


Note: the "dnl" at the end of each line has the letter "l", not the number "1" at the end of the line. And a backtick, i.e., `, is used before "" while a single quote is used after it.

[ More Info ]

[/network/email/sendmail] permanent link

Wed, May 23, 2018 10:53 pm

Dovecot restart

A user reported that she was unable to check her email today; she had also reported the problem yesterday. When I checked Sendmail, which would handle her outgoing email, by using Telnet to connect to the well-known port for Simple Mail Transfer Protocol (SMTP) on the server with telnet 25, I saw the Sendmail banner as expected, so I presumed her problem was likely with Dovecot, the software on the system that would allow her to receive her incoming email. I tried connecting to port 110, the well-known port for Post Office Protocol version 3 (POP3) connections using Telnet. When I saw the "Connected to" and "Escape character is" messages, I entered the POP3 user command followed by the user's name, but I would shortly thereafter see a "Connection closed" message every time I tried the connection with Telnet. I never saw the "Dovecot ready" prompt appear.

# telnet 110
Connected to
Escape character is '^]'.
user nell
Connection closed by foreign host.
You have new mail in /var/spool/mail/root

[ More Info ]

[/network/email/dovecot] permanent link

Fri, Mar 30, 2018 10:23 pm

Cloudmark CSI IP Reputation Remediation

I manage an email server that uses an Atlantic Broadband SMTP server as a smart host. I maintain a mailing list on the server that currently has about 1,300 email addresses. Each month someone sends a monthly newsletter to the email addresses in that list; the people associated with those addresses are all members of a retirees organization and have all indicated they wish to receive that organization's newsletter. Usually, the newsletter is transmitted without problems, but occasionally I will find that email transmitted from the server is silently discarded with no bounced emai indicating why that is occurring. Though that doesn't occur often, when it occurs, it usually occurs when the newsletter is sent. When the problem occurs, as it did yesterday, I have to request that the IP address of my server be unblocked. Initially, I would call the ISP's phone support number, i.e, an Atlantic Broadband support number, but they would in turn have to contact their email service provider, since the email service they provide is outsourced to Echo Labs as I found from examining email headers - see Email sent via an Atlantic Broadband SMTP server not being delivered. But I found that I could get the block removed more quickly if I submitted a request through Cloudmark, an anti-spam company co-founded by Vipul Ved Prakash and Napster's co-founder Jordan Ritter, which provides an anti-spam service used by Echo Labs.

[ More Info ]

[/network/email/spam/blocklists] permanent link

Mon, Feb 26, 2018 11:46 pm

Outlook reports a security problem with an encryption certificate

When I attempted to send a PKI-encrypted email message to several recipients from Microsoft Outlook for Mac 2016 (version 15.41), I saw the message "Encryption certificates for some recipients could not be found in the Outlook Contacts. Do you want to search the Active Directory servers for them?"

Encryption certificates for some recipients could not be found in the 
Outlook Contacts

I clicked on OK and then saw the message "The following recipients have encryption certificates with security problems. Do you still want to send this encrypted message?"

Outlook - encryption certificate with security problem

I clicked on Cancel and checked on whether Outlook was storing a public key certificate for the person in my contacts list. He was in the contact list, but there was no certificate associated with the person in the contacts list when I clicked on the Certificates tab.

[ More Info ]

[/network/email/clients/outlook] permanent link

Sat, Jan 06, 2018 5:01 pm

Configuring Sendmail to always allow Steam email

A family member wasn't receiving email for a Steam account she created to play a PC game. Her email comes through a Sendmail email server I manage and I found that a Domain Name System-based Blackhole List (DNSBL), the Spam and Open Relay Blocking System (SORBS), had blocked email from the IP address that Valve had for the email server used to send email to her about the account. When I checked the sendmail log file, I found the following two entries:

Dec 29 21:10:26 moonpoint sendmail[27413]: ruleset=check_relay, arg1=smtp03.stea, arg2=, [], rej
ect=550 5.7.1 Spam Block:mail from refused - see http://dnsbl.sorb
Dec 29 21:17:35 moonpoint sendmail[27661]: ruleset=check_relay, arg1=smtp01.stea, arg2=, [], rej
ect=550 5.7.1 Spam Block:mail from refused - see http://dnsbl.sorb

Checking, I found the following IP addresses and fully qualified domain names (FQDNs) for Steam email servers:

IP AddressFQDN

To ensure that none of the DNSBLs I use with Sendmail will ever block email from the Steam email servers, I added the following lines to /etc/mail/access:

Connect:                           OK
Connect:                           OK
Connect:                           OK
Connect:                           OK
Connect:                           OK

I then used the makemap hash command to rebuild the access database.

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

Once I did that, she was able to receive the Steam-related email.

[/network/email/sendmail] permanent link

Wed, Oct 11, 2017 10:20 pm

Error stating Outlook OST file is in use and cannot be accessed

After I rebooted a Windows 10 PC subsequent to a software update on the system, when I attempted to reopen Microsoft Outlook 2016, I saw the message below:

Outlook Data File

Black exclamation
mark in yellow triangle The file C:\Users\jasmith1\AppData\Local\Microsoft\Outlook\ is in use and cannot be accessed. Close any application that is using this file, and then try again. You might need to restart your computer.

[ More Info ]

[/network/email/clients/outlook/2016] permanent link

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