Capital letters in local part of email addresses

John_Gray

Has anyone experienced a problem where emails sent to
[EMAIL="Joe.Bloggs@domain.co.uk"]Joe.Bloggs@domain.co.uk[/EMAIL]
are rejected 'somewhere', whereas emails sent to
[EMAIL="joe.bloggs@domain.co.uk"]joe.bloggs@domain.co.uk[/EMAIL]
are accepted?

The only problem I've ever had with mixed-case email addresses is with sending to O2.co.uk, about 18 months ago, and I haven't had occasion to try since.

I am aware that the RFC 2821, the standard that defines how email transport works, says: 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. Mailbox domains are not case sensitive. In particular, for some hosts the user "smith" is different from the user "Smith". However, exploiting the case sensitivity of mailbox local-parts impedes interoperability and is discouraged.

However, in the very many years since the standard was written, the convention seems to have become that UpperCase characters are acceptable in the 'local part' of the email address.

Can anyone give recent real examples where this does not apply?

esuhl

I presume it depends entirely on how the mail server interprets characters. Windows is generally not case-sensitive (with filenames, at least), while Linux is. Perhaps it just depends on the OS running on the server...?

asbokid

exim, the open source mail server or "MTA", developed for Linux/Unix by the University of Cambridge, and favoured by many reputable organisations, is case-sensitive by default.

So case-sensitivity, at least for exim, but no doubt for sendmail (yuck) and other MTAs, is determined by the local server administrator.

From the Exim Specifications...

RFC 2822 states that the case of letters in the local parts of addresses cannot be assumed to be non-significant. Exim preserves the case of local parts of addresses, but by default it uses a lower-cased form when it is routing, because on most Unix systems, usernames are in lower case and case-insensitive routing is required. However, any particular router can be made to use the original case for local parts by setting the caseful_local_part generic router option.

If you must have mixed-case user names on your system, the best way to proceed, assuming you want case-independent handling of incoming email, is to set up your first router to convert incoming local parts in your domains to the correct case by means of a file lookup.......

At an individual username level on a Unix system, you could use aliasing.. so that mail for Fr3D@localhost was an alias of fred@localhost.

It's obviously not practical using aliasing when you are managing 5,000 email accounts.

However, I would expect most large organisations to use aliasing to ensure that commonly mis-spelt or mis-addressed mail that is intended for a VIP in the organisation, still reaches its destination. For example...

[EMAIL="bettywindsor@royal.gov.uk"]bettywindsor@royal.gov.uk[/EMAIL]
[EMAIL="TheQueen@royal.gov.uk"]TheQueen@royal.gov.uk[/EMAIL]
[EMAIL="QueenElizabethII@royal.gov.uk"]QueenElizabethII@royal.gov.uk[/EMAIL]
[EMAIL="elizabethwindsor@royal.gov.uk"]elizabethwindsor@royal.gov.uk[/EMAIL]
[EMAIL="brenda@royal.gov.uk"]brenda@royal.gov.uk[/EMAIL]
[EMAIL="grannywindsor@royal.gov.uk"]grannywindsor@royal.gov.uk[/EMAIL]

could all be aliases of the same mail account...

[EMAIL="elizabethalexandramary@saxecoburgandgotha.gov.uk"]elizabethalexandramary[/EMAIL][EMAIL="elizabethalexandramary@saxecoburgandgotha.gov.uk"]saxecoburgandgotha[/EMAIL][EMAIL="elizabethalexandramary@saxecoburgandgotha.gov.uk"]@royal.gov.uk[/EMAIL]