On the Add Account screen, click Advanced Settings. Enter the full domain for the provider and if you know the port include that after a colon, e.g.

You can optionally specify more detail use the following formats for security, ports and domains. Here are some of the most common combinations to try.

Incoming:
servername:993:imap4:ssl
servername:143:imap4:tls

Outgoing:
servername:465:smtp:ssl
servername:587:smtp:tls
servername:25:smtp:tls

See more information here: http://touchmail.uservoice.com/knowledgebase/articles/560385