(well priced ) Email redirection service

I recently migrated a website to a new domain , the previous hosting had email included so I needed to redirect the emails. I thought that changing MX dns records would suffice but it turned out that some server has to do the actual redirection to the new domain.

I think there may be a gap in the market, the only services I could find where either very expensive ( mailchimp ) because they offer more than just redirection or where completely free ( forwardemail.net) . The free solution might have been fine for personal use but I was doing the migration for a paying client and it just didn't feel right.

Could this be an opportunity ? Building the service seems some what straightforward, but I've heard there are complex technical issues for e-mail to work ( being listed as spam , need for rotating ip addresses ?? )

Offering only redirection service could be a good niche ?

Any thoughts would be greatly appreciated !