Tasks to try in Postosha
Postosha has a combined message list, templates with attachments, local sorting rules, spam training and a PIN for selected accounts. Connect one mailbox, find an older message, reply with an attachment and create a rule for incoming mail.
What Thunderbird offers
Thunderbird includes a calendar and add-ons. If you use these for work, decide how you will handle those tasks before switching. Connecting a mailbox alone does not transfer calendars or extensions.
Protect local data during a move
Start with one mailbox. IMAP downloads server mail again; adding the account does not transfer Thunderbird’s local archives, address book or settings. Keep the old profile until you have checked access to your important data.