things I note right off the bat:
1) You do not need your "exit loop if" statement, since you have go to next with "exit after last" checked off.
2) You do not need nested "IF" statements, you can put both conditions in one if statement:
IF [ DMonth = CMonth AND DDay = CDay]
3) I'm sure you already noticed, but "export field contents" is not compatible on a server. I believe you can do this with supercontainer though on the server if you have that plugin. I would check with 360works first though.
4) your export field step is outside the loop, so you'd only be sending the same picture as an attachment to all emails, was that ok?
5) As for the "send mail" step itself, does it work when you run it from the client? Just not from the server?
I would recommend using a plugin to do server mail tasks with. 360works' email plugin is cheap and robust.
CNS also has SMTPit for server: