When externalsender.com sends an email to a user behind PMG, he gets following spf error.
And of course he is not allowed to send mail from PMG's ip. Why is this happening?
<user@domain-behind-pmg.com>: host domain-behind-pmg.com[1.2.3.4 > (User's server ip)]
said:
550-SPF: 2.3.4.5> (PMG's...