Why don't vendors receive any notifications (PO, job request mail, confirmation mail when a new account is created, etc.)?

Hi all,

I have created vendor accounts for my active vendors and I have done all the confirmation work for them until now to fasten the procedures but I realized that I actually cannot send any notification mails to vendors. I cannot send any PO or any job request mail either. I have customized my notification templates and I can check if the vendors can receive any notifications by sending the notifications to the mail address with which I am registered to XTRF and I receive them at that mail address. When I try to do that, XTRF prompts me the pop-up message that my mail is sent but they are never received by vendors. What can be the reason for that and how can I enable them to receive the notification mails?

Thanks for your reply in advance.

Burcu