Campus Mailing Lists, Reply-to Address Errors

We’ve had reports that reply-to email addresses are being changed or sent to the wrong mail list server. e.g. replies sent to

We've found a couple of issues causing this reply-to behavior:

  1. The reply-to field is an optional field in the payload of the email that is added by an email client. Not all email clients add a reply-to field, per RFC 2822  "an optional reply-to field MAY also be included." So, the missing reply-to is caused by the sender's email client. The mandatory field is called the "Return-Path:" which is part of the email envelope; the  "Return-Path:" defines the reply address. Sympa won't 'create' a reply-to if the field doesn't already exist; it is only capable of changing an existing reply-to based on the setting described at:  
  2. The return domain rewrite is related to an organization's SENDMAIL server; in particular, an old SENDMAIL configuration. The SENDMAIL setting is causing the domain rewrite was the default behavior of older SENDMAIL versions. Ordinary SENDMAIL tries to verify the host domain to ensure it's correctly formed so it rewrites the domain name based the response from DNS. The virtual instances of the mailing list servers are defined as a CNAME to the root server's hence the reply from DNS is the canonical name which is the root server's name. As a result the lookup of which is a CNAME to has some SENDMAIL servers rewriting the domain to the canonical name/CNAME. This old feature can be turned off using the following SENDMAIL setting:  FEATURE(`nocanonify', `canonify_hosts')

Current RFCs that govern DNS configuration

RFC 5321 SMTP October 2008 - Section  2.3.5. Domain Names,  3rd paragraph

Only resolvable, fully-qualified domain names (FQDNs) are permitted when domain names are used in SMTP. In other words, names that can be resolved to MX RRs or address (i.e., A or AAAA) RRs (as discussed in Section 5) are permitted, as are CNAME RRs whose targets can be resolved, in turn, to MX or address RRs.

Section 5. Address Resolution and Mail Handling,    5.1. Locating the Target Host,  2nd paragraph

The lookup first attempts to locate an MX record associated with the  name. If a CNAME record is found, the resulting name is processed as if it were the initial name.

What does it mean?  The Campus Mailing List Service is working as designed. User's email clients govern whether a 'reply-to' is included in the email and the cause of the domain rewrite to is caused by old sendmail config.  

Keywords:reply-to domain change email error sympa   Doc ID:65340
Owner:Sympa S.Group:University of Illinois Technology Services
Created:2016-07-21 14:20 CDTUpdated:2021-03-03 01:34 CDT
Sites:University of Illinois Technology Services
Feedback:  0   0