The mailing list for listmasters using Sympa

[Victor O <address@concealed>]

Hello,

In DNS, if your domain has a CNAME attached to it, you're not allowed to have any other DNS records affiliated with that domain (i.e. CNAME cannot coexist with MX, A, etc.) Per RFC 1912 (https://www.rfc-editor.org/rfc/rfc1912.html):

2.4 CNAME records   A CNAME record is not allowed to coexist with any other data.  In   other words, if suzy.podunk.xx is an alias for sue.podunk.xx, you   can't also have an MX record for suzy.podunk.edu, or an A record, or   even a TXT record.

From experience in managing AWS infrastructure, if you have an NLB (Network Load Balancer) in AWS, you can assign a static IP address to your NLB. This gets around the CNAME problem so that you can now use an A record to point to that static IP on your NLB and your MX record can coexist with that A record.

-victor

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From: address@concealed <address@concealed> on behalf of Matthew Goebel <address@concealed>
Sent: Wednesday, February 4, 2026 3:53 PM
To: Widerski, Betty <address@concealed>
Cc: address@concealed <address@concealed>
Subject: Re: [en@sympa] Sympa DNS entries with AWS EC2 and NLB?

 

We had to get a permanent IP for our AWS sympa host - don't know how that worked I left that up to our AWS tech.

We had no issues having MX and A records pointing to the same name that I've noticed, ie something.emich.edu, but our MX records point to gmail for filtering.

Thanks,
Matt

On Wed, Feb 4, 2026 at 4:50 PM Widerski, Betty <address@concealed> wrote:

Question for sites who are hosting a Sympa server on an AWS EC2: How are you doing DNS entries for the domain name that is both the mailing address (address@concealed) and the web interface address (https://lists.my.edu)? We are attempting to migrate a Sympa server to AWS and my cloud engineers are saying that having an A record plus an MX record (which is what we did onprem using an F5) is not always functioning correctly. Plus their concern is that the NLB being used between the EC2 and the public web has 3 IP addresses that are not guaranteed to be permanently static.

 

The engineers asked if it was possible to assign the web address as like https://otherlists.my.edu leaving “lists.my.edu” as the MX for mailing. I wasn’t sure if this would break web links or list maintenance pages using the domain name variable when creating the html pages.

 

I’m not sure I’ve correctly explained this, so please ask for clarification if this is insufficient information.

 

Thanks

Betty

 

 

Betty Widerski

Cloud & Server Engineering – HBS Information Technology

HARVARD  BUSINESS  SCHOOL     

Shad 108 N | address@concealed | T: 617.212.3056

 

 

 

--

Matthew Goebel : maddress@concealed : Unix Jockey @ EMU : Hail Eris
Neo-Student, Net Lurker, Donut consumer, and procrastinating medher...
 "Always with the negative waves, Moriarty" - Oddball
 "Comfort the troubled, and trouble the comfortable." - Dietrich Bonhoeffer

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