Mail Server not accepting attachments in KB

I am using sendemail, it works fine for sending non rtf files that are about 67 bytes, but the generated rtf file is 5-6 KB hence gets sent in segments not by one single packet, and email server only sends acknowledgement TCP packet to the first segment of the msg and never to the rest, that’s why sending this attachment fails. Tried other email clients with same behavior. Looks like either a network or email server size limitation issue. Anyone had any luck recently? I used same commands in available walkthrough which is strange.