Ok gang perhaps one of y'all can help enlighten me. One of our customers had his allocated space fill up on his account during a big sale due to the server logfile getting to large. As a result when he logged into his e-mail this am he had none. Does the excess e-mail get bounced back or go to e-mail heaven? Or is it possibly somewhere else? This is fairly important as the e-mails are orders! Thanks for any help you can provide!

mail is stored in /var/spool/mqueue on various Linux/Unix/Solaris webservers. Unfortunately Apache likes to write it's logfiles to /var/log/httpd (Yuck). This means that your apache logfiles can fill the entire /var partition if unchecked.

Anyways to answer your question:

Once the partition and/or disk is full sendmail can not write to the disk. If this continues for any sustained period of time the emails are lost forever- Gone :(

Would this be the case if this was a resold account rather than an entire disk being full? Essentially he simply went over his alloted space for his account. Overall we are fine for space.

It also depends on what MTA is in use.

qmail will return a temporary error when the disk is full, so the sending MTA will attempt delivery again later.