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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 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

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 verizon.net address and I needed to convert the "from" address from a verizon.net 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/sendmail.mc. For the example below, I use the example.com domain as the local domain name for the server.

MASQUERADE_DOMAIN(`verizon.net')dnl
MASQUERADE_AS(`example.com')dnl

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 "verizon.net" 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 mail.example.com 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 127.0.0.1 110
Trying 127.0.0.1...
Connected to 127.0.0.1.
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
mpowered.com, arg2=127.0.0.6, relay=smtp03.steampowered.com [208.64.202.39], rej
ect=550 5.7.1 Spam Block:mail from 208.64.202.39 refused - see http://dnsbl.sorb
s.net/
Dec 29 21:17:35 moonpoint sendmail[27661]: ruleset=check_relay, arg1=smtp01.stea
mpowered.com, arg2=127.0.0.6, relay=smtp01.steampowered.com [208.64.202.37], rej
ect=550 5.7.1 Spam Block:mail from 208.64.202.37 refused - see http://dnsbl.sorb
s.net/

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

IP AddressFQDN
208.64.202.36 smtp.steampowered.com
208.64.202.37 smtp01.steampowered.com
208.64.202.38 smtp02.steampowered.com
208.64.202.39 smtp03.steampowered.com
208.64.202.40 steammail.steampowered.com

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:208.64.202.36                           OK
Connect:208.64.202.37                           OK
Connect:208.64.202.38                           OK
Connect:208.64.202.39                           OK
Connect:208.64.202.40                           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\john.a.smith@exmple.com.ost 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

Wed, Sep 06, 2017 11:57 pm

GoDaddy continues to show "Loading..." when composing email

Someone who uses GoDaddy for her email reported to me today that she couldn't send email. I logged into her account from another system and was able to send email to myself. When I notified her that I had been able to send email from her acount to myself, she sent an email to me, but reported it was still stating "loading" when she hit the send button. So tonight I logged into her system and opened the Firefox browser, since she uses that browser to send and receive email. When I clicked on Compose, I saw a "Loading..." message in the body of the email that wouldn't go away unless I clicked on the Plain Text tab to switch from "Rich Text", which allows one to format text in the message with bolding, font colors, etc., to "Plain Text". But when I switched back to "Rich Text", I had problems typing my email address in the "To" field with only one letter appearing in the "To" field no matter how many letters I typed.

[ More Info ]

[/network/email/godaddy] permanent link

Sun, Sep 03, 2017 10:36 pm

SORBS blocking email from AOL

I manage a Linux server that functions as an email server using the free and open source software (FOSS) package sendmail. I provide a mechanism through the server for someone who has Verizon as his Internet Service Provider (ISP) to send monthly newsletters by email to an organization that has about thirteen hundred members on its email distribution list, since he can't send to that number of people through his ISP-provided email service. I do so by providing an email alias on my server, e.g., thelist@example.com that he puts in the BCC line of his email. The alias is stored in /etc/aliases and points to a text file containing the list of all members' email addresses. So his ISP-provided SMTP server sees only the one address, thelist@example.com, which results in an email message to the server I manage that then translates that address into the approximately 1,300 email addresses of members and sends the newsletter to all members.

But this month the user reported he had sent the message, but it had not been delivered to recipients. I first checked the server's mail log, /var/log/maillog, for any occurrences of his email address for the day he reported the problem. I use several free DNS-based Blackhole List (DNSBL) services to reduce the amount of spam that reaches user's inboxes, so I suspected that one of those services had blocked email from the SMTP server through which he was sending his message, even though I had whitelisted his email address quite some time ago by adding a line like the following one to /etc/mail/access and then running the command makemap hash /etc/mail/access </etc/mail/access.

slartibartfast123987@verizon.net	OK

I didn't find any references to his email address in the /var/log/mail file, so I asked him to resend the message. I still didn't see any references to his email address in the /var/log/maillog file, but I did see that SORBS had blocked email from an America Online (AOL) server at the time he sent the message.

[ More Info ]

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

Tue, Aug 15, 2017 10:07 pm

Saving an email message to a file in mutt

Mutt is a text-based email client for Linux and Unix-like systems. If you want to save a particular message to a file in mutt, you can select the message then hit the v (the lowercase letter) key. In mutt, the letter is used for "view-attachments", but you can also use it to save the body of an email message to a file. If you hit the s key with the message selected or while viewing the message, you will see "<no description>" next to the number 1. If the email has any attachments they will be numbered from 2 upwards. With the first entry, i.e. the one labeled "<no description>" selected, if you hit the letter s (lowercase letter), you will see "Save to file:"

Mutt - save to file

Type the file name you wish the message to be saved under after "Save to file:" After saving the file, you can hit q several times to get back to the shell prompt. The message will be in the current directory. The file will only contain the contents of the message, not the message header, i.e., you won't see from, to, and subject lines.

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

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