I had to remove the domain from mydestination in PostFix then reload PostFix- ALL IS GREAT THANK YOU VERY MUCH!
EDIT 2: It appears that ALL E-Mail being sent to the domain 'giganetwireless.net' is seeing a response from PostFix OR ISPConfig claiming 'unknown user' at the domain giganetwireless.net.
After regaining access to SquirrellMail I logged into a users account and sent an E-Mail out to one of my Gmail accounts successfully.
From Gmail however when I try to reply I receive an error notice:
I tailed '/var/log/mail.log' while Gmail attempted sending to the giganetwireless.net server- following is the results of that:
Jun 3 17:47:00 giganetwireless postfix/smtpd: connect from mail-ew0-f219.google.com[126.96.36.199]
Jun 3 17:47:01 giganetwireless postfix/trivial-rewrite: warning: do not list domain giganetwireless.net in BOTH mydestination and virtual_mailbox_domains
Jun 3 17:47:01 giganetwireless postfix/smtpd: D3273B8C1E8: client=mail-ew0-f219.google.com[188.8.131.52]
What could be the cause of this strange behaviour?
Thank you for your suggestions.