Technically SMTP extensions are case-insensitive

[ARitz-Cracker]

As stated in RFC5321

Although EHLO keywords may be specified in upper, lower, or mixed case, they MUST always be recognized and processed in a case-insensitive manner.

No observed SMTP server seems to list its extensions in lowercase, but it's still something to consider to ensure maximum compliance

[xpepermint]

PR?

[ARitz-Cracker]

Soon™ as I personally don't consider this critical. I'll leave this issue open as a reminder to myself, though anyone's invited to implement the patch.