Again, IMAP and POP3 are both the receiving protocols. Whichever one your mail provider uses for you to fetch email from them, the protocol that you use to send email out is SMTP of some form.
SMTP with the older security mechanism usually termed “SSL” (though it’s not really) usually operates on a dedicated port number 465, whereas the newer STARTTLS mechanism uses 25 or 587 - if it doesn’t work on 587 try 25 or vice versa.