> The next thing you can do, instead of paying for whitelisting, ist to contact the mailserver-admin at system you are trying to deliver mail to. This can be a

> The next thing you can do, instead of paying for whitelisting, ist to contact the mailserver-admin at system you are trying to deliver mail to. This can be a bit of a hassle - seeing that your mailserver just got blocked - but it usually works. The same way systems don't want to receive SPAM they also don't want to overblock, after all they want their users to receive emails as well. If you are the mail admin of a sending system and you're reaching out to the receiving system this is usually a pretty good indicator that you don't want to spam them. That's nice in theory. In practice, UCEPROTECT level 3 is used by, for example, all Microsoft properties (including hotmail, etc). And UCEPROTECT level 3 lists a lot of netblocks. So, if you want to send e-mail from, say, Digital Ocean, to any Microsoft managed e-mail domain, you can just forget about it. DO doesn't care, Microsoft very much doesn't care. Good luck trying to contact a postmaster there!