Pix 506E appears to be blocking SMTP all of the sudden?

For some reason late last night we weren't able to send mail to our smtp server... it just timed out... i originally thought it was the mail server - but it's running fine inside our network - i can send smtp all day long.  So i'm lead to believe it may be the pix... however i haven't changed anything in our config in a long time and everything has been smooth, i tried restarting the pix and still no go.... the smtp & pop3 are the same machine, and the users can download all of their email, just smtp times out...  any ideas- it seems to be a network issue somewhere?

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Did your ISP change anything? Did they start blocking port 25?
If it's been working fine and no configuration changes have been made, then it is most likely not the PIX.
If ANY configuration change was made, then I would suspect a typo or something.
Did anything change on the server? Did anyone disable smtp relay? Does it require a valid login to send mail?
Do you receive email from external sources?
The problem is only with POP3 clients not being able to send mail, although they can receive mail OK?

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NickUAAuthor Commented:
lrmoore you are correct...Cox started wanting their customers to use their smtp server.

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