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[ietf-smtp] Email address maximum length

2019-11-23 01:32:47
This errata <> sets the maximum
email address length to 256 characters.

This errara <> seem like corrected
that part and now the maximum email address length is 254 characters.

I have tested major mail services like Gmail, Outlook and YahooMail for RFC
email address length compatibility.

interestingly, they are all going like




Gmail seem like it accepts mail when the email address length is up to 900

I was able to successfully deliver mail using the following 900 character




327 characters.

I have no idea how they came to that number.  I hope that's not an
arbitrary number.

I was able to successfully deliver mail using the following 327 character



I'm more concerned about the local-part limitation set by RFC.

RFC 821 says:

The maximum total length of a user name is 64 characters.

RFC 2821 says:

The maximum total length of a user name or other local-part is 64

RCF 5321 says:  Local-part
The maximum total length of a user name or other local-part is 64

It's been almost 4 decades since RFC 821.  The world has changed so much
since.  So It doesn't make any sense to stick to that 64 character limit.

Variable Envelope Return Path (VERP) and Sender Rewriting Scheme (SRS) are
2 perfect examples where 64 character limit actually causes issues.



If sticks to the RFC limit 64 characters and a user from
picked a 64 character username, then the above VERP address structure won't


SRS uses similar structure to avoid SPF failures. Microsoft seem like
recently adopted
SRS in their office 365 product.

Where HHH is "hash-based message authentication code", computed against a
local secret, but only a part of it is used.

SRS1 rewriting an already rewritten address, in a multi-hop scenario.

So the address would look like

since SRS1 incorporates 2 domains in the local-part, 64 characters are not


I think we are still sticking to that number 64 because it was defined in
RFC 821.

Is there any valid reason why we still need that limitation?  If not, Can
we remove that limitation?

Look forward to hearing your thoughts.

Thanks very much.

Best Regards,

Viruthagiri Thirumavalavan
Dombox, Inc.
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