When mail software tries to send an email to your domain, upon issuing the SMTP "RCPT TO" command, there is an extremely long delay.

CAUSE:

This happens because the mail server is trying to do a DNS blacklist lookup on the sender of the email and for some reason the DNS lookup is taking a long time.

LIKELY CAUSE:

Most likely the DNS blacklist service that you are using such as http://dsbl.org/ is no longer in service.  This is causing your timeouts.

LIKELY RESOLUTION:

Remote the offending DNS Blacklists from MailEnable.  To do that:

1)  Click on Start > Programs > Mail Enable > Mail Enable Administrator

2)  In MailEnable expand MailEnable > Servers > LocalHost > Connectors.  Right-Click on SMTP and select "Properties".

3)  On the DNS BlackListing Tab remove all "DSBL" entries and click "OK".

Your issue should be resolved.