My mail client cannot connect

Check the port first. 993 for IMAP and 465 for SMTP, both SSL/TLS. Many clients default the outgoing port to 587 and it will not connect — nothing listens there. A client set to 25 will fail too, and many networks block that port outright.

Then check the username. It is the whole address, not the part before the @ — a client that autofilled just the local part is the single most common cause of an authentication failure.

If both are right and it still fails, try from a different network. Some office and hotel networks block outbound mail ports entirely, which looks identical to a wrong password from inside the client.