You may have issues though if your ISP blocks port 25 SMTP.
Some ISPs require encrypted email communication on port ~993 and you wont be able to do that on an arduino.
If the ISP does block outgoing mail (which I think they should), they likely have their own SMTP server you can use to relay the email. In a way this makes it even easier, since you can just connect to their email server for every email you want to send and leave it up to their SMTP server to relay it to the correct next hop (saves you from having to send DNS queries from your AVR).
Port 993 is IMAP over SSL - you can't submit email via IMAP. What some mail servers support however is storing a message via IMAP in your 'outbox', after which the mail server picks it up and sends it wherever it needs to go. If my provider forced me to do this, I would cancel my service and switch to another provider (after letting them know why they lost a customer).
There are also providers that require you to authenticate yourself (somewhat non-standard) before being allowed to submit email via SMTP or that require you to first set up a POP or IMAP connection, before you are allowed to connect to their SMTP server (port 'knocking'). In both cases they do this so they can see which customer it is that is trying to send an email.