Wow Izzy, I see a lot of people asking for help with mail services and you seem to be the one with the know how on this subject, I wonder if your posts could be collected or you could write a guide on the subject of mail usage and or configuration and a moderator could pin it?
I'm sure the new users would appreciate this and it could even be translated to the other common languages found here?
I'm not sure but for me there was confusion over the use of mercury mail being the primary service for all mail but it would seem to me mercury mail is used if you want to have a mail service such as yahoo of google? See I'm still not really sure about that.
SMPT seems to be what sends all mail notifications for things like new posts and pms for phpbbs and maybe for mailing news for some sites when you want to mail a whole list of subscribers...?
Anyway maybe I way off here and apologize if so, I just see people getting stuck just as I did and you seem to be the one that points people in the write direction, i've even pointed a few in the same direction you pointed me in.