[BlueOnyx:23934] Re: Recent problems with mail delivery to some domains

[Ken Hohhof]

Before looking at technical fixes, I would first ask if I have mail
customers whose credentials have been compromises and are being used to send
spam.  This will get your server IP blacklisted for sending spam.  Are you
sure the webpage they are sending you to via the SMTP error code isn't
helpful?  I've seen some that tell you exactly why they are refusing mail
from you.

 

I suspect that SPF, DKIM and DMARC will be of little to no use in solving
this problem.

 

You could also check your mailserver IP address for blacklists at a site
like https://mxtoolbox.com/blacklists.aspx

 

From: Blueonyx <blueonyx-bounces at mail.blueonyx.it> On Behalf Of Chuck Tetlow
Sent: Wednesday, June 3, 2020 5:12 PM
To: BlueOnyx Mail List <blueonyx at blueonyx.it>
Subject: [BlueOnyx:23933] Recent problems with mail delivery to some domains

 

Hello BlueOnyx experts,

 

Has anyone suddenly had problems delivering email to some domains - mostly
Hotmail, Outlook, and other Microsoft domains?  Over the last couple of
weeks - I find that I suddenly can't send email to Hotmail.  It bounces back
every time with a logged "service unavailable".  And the bounce error
message leads to a webpage with a very vague explanation - and essentially
no way to fix it.

 

I'm also beginning to get multiple inquiries from my customers - when their
users can't send mail to M$ domains.  So I've got to find a resolution. 

 

I've checked multiple sources, and neither the domain or the IP address is
blacklisted.  I've checked forward and reverse DNS records - all are
correct.  I already had a loose SPF record, now have tightened that up - no
difference.  So I went out to get info on DMARC - and created a DMARC
record.  Still no help.  Every message fails.

 

I considered (briefly) DKIM - but that seems to be a challenging system,
which appears to require changes to the MTA.  And I just don't know if
BlueOnyx supports DKIM, or will allow Sendmail to be modified to use DKIM.

 

So questions: Has anyone else experienced this problem with
Hotmail/Outlook/Microsoft.com/etc?  And has anyone found a resolution to the
problem?  I'd love to hear about your fix!

 

Second.  Does anyone know if we can implement DKIM in BlueOnyx?  I suspect
that sooner or later - everyone will HAVE to go to DKIM.  As more and more
strict SPAM fighting measures are put in place - I believe DKIM will be the
ultimate solution to combat spoofing FROM addressing.

 

Thanks everyone.  I appreciate any suggestions on fixing this problem.  

 

 

 

Chuck

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.blueonyx.it/pipermail/blueonyx/attachments/20200603/a0b55da4/attachment.html>