[Ashur]

for the most hosts i worked with default SMTP should work fine i.e. using an up to date host that translates requests automatically even if smtp actual server is on different machine
but some hosts offer a separate SMTP server linkup and setup

if you got no clue about SMTP server then here is a probably hint if your SQL server on same hosting server there is a smaller chance that your SMTP is on different server

if you're hosting your own server then everything should be default unless you forgot to setup a SMTP server or didn't set it up properly

for the attachments are you saying that TSSE asking you for username and password or the httpd service asking a username and password?