Checking Email Blacklist and Getting Delisted

What do you do when your email server has been blacklisted and you are unable to send emails to certain domains? It’s best to be proactive and not get on the blacklists in the first place, but in the unfortunate event you do get blacklisted, here are some notes.

Checking Blacklists

First thing is we need to see which lists we are on. There are a couple of services that check multiple blacklists

These should give you an idea of which ones we need to go request a delisting. (,

AT&T is tricky as they don’t have an online site to show if you are blacklisted or not. They don’t seem very responsive and it can take awhile.

Send an email to “” with your Mail Server IP address, the domain and ask to be delisted. You should get an auto-reply and then they usually will do something about it in 24-48 hours

More information below

Other Blacklist

These are all fairly straight forward to check out. Some of them you will need to enter in an email, or maybe set up an account, others are as simple as requesting the IP to be delisted.

How to Send an Email using Telnet

We’ll be using telnet to connect to a mail server and send ourselves an email.

The parts in bold are the commands to enter.

[bob@linux ~]$ telnet 25
Connected to
Escape character is '^]'. ESMTP Exim 4.85 #2 Mon, 09 May 2022 22:12:59 
220-We do not authorize the use of this system to transport unsolicited, 
220 and/or bulk e-mail.
250 Hello []
250 OK
250 Accepted
354 Enter message, ending with "." on a line by itself
Subject: Test Message

This is a test

250 OK id=5a1g7i-1347MT-1p
221 closing connection
Connection closed by foreign host.

Further links to read

How To tell if an email on a cPanel server has been read from the command line

All of the emails in the email directories contain one of the following at the end of the filename

$ ls cur/ | cut -d: -f 2 | sort | uniq -c
54 2,               <- Not Read
12 2,ab             <- Not Read
83 2,S              <- Read
61 2,Sab            <- Read

The first two “2, and 2,ab” mean that the message has not been read. The bottom 2 “2,S and s,Sab” mean that the message has been read or “seen?”. Guess that is what the S is for. Not sure what ab is for.

imapsync – NO [OVERQUOTA] Not enough disk quota

msg INBOX/4624 {75129} couldn't append  (Subject:[Email message]) to folder INBOX: Error sending '55 APPEND INBOX (\Seen) "25-Aug-2017 09:12:05 -0600" {75129}': 55 NO [OVERQUOTA] Not enough disk quota (0.001 + 0.000 secs).

To resolve the above problem, check the following

  1. Email mailbox allocated size
  2. cPanel account user Quota

The above problem was due to the fact that the cPanel User Quota was maxed out. Increasing the space allocated to the account resolved the problem.