We are using Zoho Mail in our company and so far the experience was great. But recently we have faced an issue of not getting our emails delivered to the new company we are now working with. One of the recent returns' errors was:
ERROR_CODE :550, ERROR_CODE :5.7.1 There is your IP address in BLACK LIST. Check at www.sorbs.net/lookup.shtml
I've contacted the recipient's administrator but have been told that since we are using a public mail service it's quite natural that some of the IPs might be in the blacklist and that he cannot whitelist our specific domain name but specific IPs only. Since the IPs are different through the day, I'm not able to obtain the list of all IPs of the mail server and I'm not sure how frequently and when they are getting updated so that I can't keep the recipients informed as well.
In order to check the deliverability to the recipient's server I've also tried to drop them an email using my personal Yahoo Mail but surprisingly for me I've received the same error back and again the same reply from the administrator - Yahoo Mail is a public mail server and the SORBS reports spam / viruses getting detected on the IP my email was sent from.
The problem is that I'm not sure how we can handle it and how may I ensure our emails are getting delivered. For now it looks like any mail provider I use will be public and have / might have the same issue for us. But at the same time I'm unable to establish our own private mail server just for the purpose since it's going to be quite complicated.
The company we are working with is large and worth trust so I'm sure that their server is working like the swiss watches, but I don't feel that the problem is at our side either. So I'm looking for an advice or a recommendation of a service that might help to solve the issue. Let's say some sort of mail redirection service with static personal IP, so that we can continue to use the public mail service but at the same time be sure that we have dedicated personal IP and are responsible for it being in the whitelist. Please advice.