Neither of those two describe how to lowercase the extension part – that’s a bit the point. One puts info that they use LMTP, another decides to link LDA docs, and even quoting how to lower the extension part, despite that isn’t actually possible in LMTP in a similar manner.

I’m sure the OP had used google prior, and didn’t find any useful information, which is why the question got asked in the first place.

Since you’ve linked the LTMP docs, can you point out where in those docs, it explains anything with lowering the extension part? I can’t find it in the two links.

From: dovecot <dovecot-bounces@dovecot.org> on behalf of Benny Pedersen <me@junc.eu>
Date: Sunday, 22 May 2022 at 12:26
To: dovecot@dovecot.org <dovecot@dovecot.org>
Subject: Re: Fix lmtp_save_to_detail_mailbox to be case insensitive?

On 2022-05-22 11:33, Lucas Rolff wrote:
> Wouldn’t it be ideal to link to a LMTP documentation page that
> describes how to do the same thing under LTMP, and not link to LDA?

typo :)

https://doc.dovecot.org/configuration_manual/protocols/lmtp_server/

https://wiki.dovecot.org/HowTo/PostfixDovecotLMTP

is google not our friends ? :=)