Trying to send/receive by "synchronising bin" prevents receiving or sending

I don’t know which type of account you are using (IMAP / POP3 or Exchange), but normally when Outlook is synchronizing for a long period it may be because the mailbox contains too many emails, and therefore it “has to re‑index all the messages,” which can delay the process. Another possible issue is the synchronization frequency. I once saw a case where someone had configured Outlook to synchronize every 5 minutes, but since there were many emails, the process entered an endless loop and the person never received new messages because each synchronization started before the previous one had finished.

Other possible causes to consider:

Very large folders (Deleted Items, Junk, Sent Items) slowing down synchronization.

Corrupted OST/PST file causing Outlook to hang.

Third‑party add‑ins interfering with send/receive.

IMAP accounts syncing all folders, including “Bin” (Trash), which can take a long time.

Unstable internet connection forcing Outlook to retry synchronization.

Antivirus or firewall blocking communication with the mail server.

Outdated Outlook version with known bugs.

Mail server changed the ports or configuration as certificantion

Try this:

Increase the synchronization interval to 15–30 minutes.

Empty or archive large folders.

Use the ScanPST tool to repair OST/PST files.

Temporarily disable add‑ins to test.

Update Outlook/Office to the latest version.

Test the account in another mail client to confirm if the issue is server‑side or Outlook‑related.