SMTP technical details

I have a UNIX host that sends email via SMTP with a c language script I wrote.  The script was sending out the FROM command like this:

"MAIL FROM: name <name@host.com> \r\n"

It has worked for years until just the other day it sputtered then stopped alltogether.

I changed it to this:

"MAIL FROM: name@host.com \r\n"

and all is well.  Any idea why all of the sudden this would be invalid?