Sender Callout Verification - ?
One of my friend is facing problem sending mails to one particular domain. The mails get bounced back with 451: Sender Callout Verification Failed. My friend is using shared hosting email services.
Whereas when I send mail from my two servers (Perfect Server: Ubuntu 8.04 and Zimbra running on Ubuntu), the mails get delivered properly.
I googled for 'Sender Callout Verification', and found that the recipient server verifies the sender by sending mail to sender's outbound server.
I want to know, what should I ask the email hosting provider to get the mails deliver properly to recipient. Do they need to allow incoming mails to their outbound server or need to allow incoming mails from null sender on outbound server or need to open Port25 on outbound server.
Thanks in advance.