Thunderbird can delete mail from the server after a number of days when using POP. IMAP users usually do not need this — the server and devices stay in sync until you delete mail yourself.
POP only
- Open Thunderbird → Account Settings → your POP account → Server Settings.
- Enable leave messages on server if you want a temporary copy, and set delete after XX days.
- Save and compact folders if prompted.
Tip: Prefer IMAP for everyday use so webmail and phones match. See the Thunderbird IMAP guide.
