IETF RFC 5321 bug / violation: UPPER CASE modified email


During the last few years i noticed that Blizzard’s systems are MODIFYING the user-provided email address when sending messages by converting the email address to UPPER CASE and it’s starting to become irritating.

The email address itself is properly defined as lower-case in my Battlenet account, but your servers are modifying it and it gets converted to upper case when i get any email from Blizzard. (i checked the full SMTP headers too.)

In addition to looking awfully like SCREAMING when viewing any email messages addressed to me by Blizzard, while using any mail client (and in SMTP headers), this is an IETF RFC 5321 Standard violation because email addresses are CasE SEnsITivE as defined in the standard (-yes, even if many email servers will treat them as insensitive, for convenience of use-) and converting them to UPPER CASE when sending messages to users might / will break some email servers when delivering those messages.

This will potentially result even in locking those respective users out of their game accounts because email addressed to them might not reach the correct mailbox.

Looking back through my messages received from Blizzard, the problem with your use of SMTP seems to have started in 2016.

  • March 5th, 2016 is the last email message that i received that was addressed correctly
  • on March 8th, 2016 the emails started to arrive from Blizzard with the local-part of the email address in ALL UPPER CASE.

Please note that RFC 5321 section 2.3.11. “Mailbox and Address” says:

Consequently, and due to a long history of problems when intermediate
hosts have attempted to optimize transport by modifying them, the
local-part MUST be interpreted and assigned semantics only by the host
specified in the domain part of the address.

and further, in section 2.4. “General Syntax Principles and Transaction Model” it specifies that:

Verbs and argument values (e.g., “TO:” or “to:” in the RCPT command
and extension name keywords) are not case sensitive, with the sole
exception in this specification of a mailbox local-part (SMTP
Extensions may explicitly specify case-sensitive elements).

The local-part of a mailbox MUST BE treated as case sensitive.
Therefore, SMTP implementations MUST take care to preserve the case
of mailbox local-parts. In particular, for some hosts, the user
“smith” is different from the user “Smith”.

Thus, interpreting and modifying the email address that was entered by the user is not allowed by the IETF Standard, even if the mail server itself might be tolerant of capitalization errors when an address is entered manually.

Please fix your mail servers, 5+ years of malformed email delivery (2016 - 2022), almost 6 years now, is too much already.