Exchange Server 2003

Question

Dear Expert,

We have a scenerio of network in which our front-end exch server is connected with our ISA firewall for e-mail forwarding.

but since yesterday we are getting an issue in sending mails to external domains. the problem is that while sending the user gets different undelivery message eg. " There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <albakri #5.5.0 smtp;550-"JunkMail rejected - fmicex.fmic.org.af (albakri) [202." since we haven't brought any changes in our firewall either right now we are only able to send to some few external domains like gmail.

Please provide your kind support on this ASAP.

Many Thanks,
Aryan khan