It has most likely nothing to do with InterForm400.
The problem is probably, that the E-mail size is 128 Kbyte or more. By default the iSeries split-up mails into pieces of 128 Kbyte. The 128 Kbyte can by increased up to 2048Kb or even *NOMAX with the command, Change POP Server Attibutes:
Re: E-mail from InterForm400 is split up
It has most likely nothing to do with InterForm400.
The problem is probably, that the E-mail size is 128 Kbyte or more. By default the iSeries split-up mails into pieces of 128 Kbyte. The 128 Kbyte can by increased up to 2048Kb or even *NOMAX with the command, Change POP Server Attibutes:
CHGPOPA MSGSPLIT(*NOMAX)
(Here the value is increased to *NOMAX).