Dirk St?cker: > For some subdomains when switching from catchall to individual settings I > simply set a CNAME to another name with correct MX settings > > name.domain.tld --> mail.domain.tld (containing A,AAAA and MX) > > It worked for many servers, but some started to deliver mail to > u...@mail.domain.tld instead of u...@name.domain.tld. They shouldn't > rewrite the mail address, should they?
That goes back to RFC 821. RFC 2821 explicitly allows aliases in commands. Postfix still has a now-unused smtp_unalias module to replace domain name aliases in MAIL FROM and RCPT TO. RFC 821: 3.7. DOMAINS Whenever domain names are used in SMTP only the official names are used, the use of nicknames or aliases is not allowed. 4.1.2. COMMAND SYNTAX Hosts are generally known by names which are translated to addresses in each host. Note that the name elements of domains are the official names -- no use of nicknames or aliases is allowed. RFC 2821: 3.6 Domains 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 A RRs (as discussed in section 5) are permitted, as are CNAME RRs whose targets can be resolved, in turn, to MX or A RRs. Local nicknames or unqualified names MUST NOT be used. There are two exceptions to the rule requiring FQDNs: - The domain name given in the EHLO command MUST BE either a primary host name (a domain name that resolves to an A RR) or, if the host has no name, an address literal as described in section 4.1.1.1. Wietse