There are several potential reasons why you are not receiving the email
in question. To know with certainty what the exact reason is we will
need to see the bounced messages that the sender is receiving, if any.
If the sender gets a bounce-back to their message please forward this to
firstname.lastname@example.org. This will help us to identify the cause of this problem.
Once reason why email is not being received is that it has been
classified as being "SPAM" by our Barracuda Mail Filters/CanIt Spam
Filters. Another likely reasons is that our mail server is rejecting the
incoming email based on the fact that the sending server is listed in
one or more of the RBLs (Realtime BlackLists) that Alentus subscribes
to. RBLs are used to identify sources of spam and are used to limit the
amount of spam received by our customers.
If it is determined that this is the problem there are a few potential solutions, as follows:
1. Have the sender send their email via a different SMTP server.
2. Have the sender send their email from a different email address.
3. Have the administrator of the sending SMTP server fix their server such that it is no longer blacklisted.
4. We can disable spam filtering for your domain to ensure all email
arrives, but this will lead to a significant increase in the amount of
spam you receive.
The RBL that Alentus currently uses is
zen.spamhaus.org (http://www.spamhaus.org/zen/). You can check if your
SMTP server is on a given blacklist by using the following link: http://mxtoolbox.com/blacklists.aspx. You will need to know the IP address of the sending server to check the blacklist.