We use Exchange mail server. All our dns records are available including DMARC and DKIM. However, even though we are not in any Blacklist, some of our customers try to send e-mails as follows and not receive mails. With "sorbs.net", we have emailed many times and stated that they do not come from their own address and that our ip addresses are not in their database and that we call the problem in the outside world by showing a few examples. But they didn't come up with a solution. For example: any one can send an e-mail to a yahma or yahoodan company e-mail address, while the other person cannot assign and give the following error. The next day or 2 hours later, when you try, it freezes to normal, but then it gets back to its normal state for a while. Has any of these problems come up and found a solution? Thank you.
"550 5.7.1 Your IP is on the sorbs.net block list"
Unfortunately if the accepting server is bouncing your email because it thinks your IP is on a blacklist (sorbs in this case), there really is not much you can do.
It sounds like you are taking all the right steps to try to remove it, and really contacting sorbs is the ultimate goal. If this is a continuing problem with the same recipients, you can have them ask their IT admins to whitelist either your domain or IP to ensure your mail is delivered.
This type of situation is a very frustrating one to be in, as you are clearly doing everything you can, running DMARC and DKIM and following the right standards, but an external party not accepting your mail because of a ip showing up on a blacklist is something that is entirely outside of your control.
Have you been in possession of the IP for a long time? Is it dedicated?
Regardless, continue to do what you are doing, perhaps contact sorbs and see if they can give you any more details.
Goodluck, i wish there was a more definitive way to pursue this, but there is not.