I’ve been having an odd problem with being unable to delete emails from the Inbox of my self-hosted email account from my Android phone, using the Gmail app, using IMAP. When I would delete a message, a copy would be created in the Trash folder, but the original would remain in the inbox – when viewed from webmail. When I refreshed the inbox, the original would reappear on my phone.
At first, I thought the problem was permissions on /var/mail – so I did various changes such as chmod 1775, but to no avail.
I then remembered that I had recently re-setup my mail account on my phone, and realized that maybe it wasn’t using IMAP previously. So, I deleted the account, set it up again as POP3, and enabled server-side deletion. It worked!
It turns out that most mobile IMAP clients do not support the ability to achieve true server-side deletion. Using POP3 is an easy alternative and there is no harm. Yes, POP3 is an outdated and cruddy protocol, but in the end, it works.