[MM3-users] Re: hello， Discussion on how to subscribe to themailing list

朱超 writes:

Some MUAs are very old , and allowed from RFC2821 and not allowed from RFC5321.

August 1982 old? RFC 821 "Simple Mail Transfer Protocol" dated August 1982, section 4.5.3. "SIZES" provides the following guidance:

[E]very implementation must be able to receive objects of at least these sizes, but must not send objects larger than these sizes.

• TO THE MAXIMUM EXTENT POSSIBLE, IMPLEMENTATION TECHNIQUES WHICH *
• IMPOSE NO LIMITS ON THE LENGTH OF THESE OBJECTS SHOULD BE USED. * user: The maximum total length of a user name is 64 characters. domain: The maximum total length of a domain name is 64 characters.

At least the example you give satisfied those minimum requirements (61 characters in the local-part, don't know how many in the domain but 64 is a lot), so the MUA(s) you're dealing with don't conform to the earliest reasonable specification.