Mailgun's Sending IP 198.61.254.54 is currently listed on SORBS. Support haven't responsed to my ticket. What do I do?

Question

On Monday morning messages sent via MailGun to our Office 365 account started to fail with the following message:

5.7.511 Access denied, banned sender[198.61.254.54]. To request removal from this list please forward this message to [email protected]. For more information please go to  http://go.microsoft.com/fwlink/?LinkId=526653.

I checked on MX Toolbox and found their IP 198.61.254.54 listed in SORBS.

I cannot delist the IP from SORBS as the request has to come from the IP address which is listed.

I emailed the delist@ address at Microsoft, who replied to say that the ISP/ESP is responsible for delistings.

I opened a ticket on Tuesday at 15:11pm with Mailgun support, asking them to delist the IP or change us to a different IP. It's now 15:42 on Wednesday and they have not acknowledged or replied to my ticket.

We send around 5,000 emails per month so are well under their recommended 50k+ threshold for a dedicated IP address.

Mailgun's control panel says:

For technical questions we recommend asking the community on Stack Overflow.

So here I am. What's my next move?

Answer 1

Mailgun support responded after 51 hours and said: "We have reviewed the error, and we have made adjustments on our side that will help solve this issue moving forward".

They had changed the shared IP address my domains were allocated to, and now mails are being delivered again correctly.

Another possible solution to this would have been for me to purchase a dedicated sending IP, although I was close to the lower recommended limit for this so I'm not sure if they would have improved deliverability in my case. I'm not sure if the purchase process for dedicated IPs is automated, or if I would have had to wait for a support agent to assign the new IP in any case.