Don't associate your regular email domain with e-mail campaigns
However well maintained and legitimate the distribution lists, any sufficiently large mailing may be classified by sufficient people and/or systems as spam that it can result in blacklisting you regular e-mail.
You don't want to deal with either sending large volumes of mail using your regular infrastructure, interfering with regular mail traffic, nor with large numbers of bounces.
So instruct your marketing people they can't use an
@example.com email address for their campaigns, nor the regular mail servers.
Seperate marketing domain
Create either a subdomain e.g.
campaigns.example.com or register a new domain
example-campaigns.com and set up the MX records and such according to the specs of your third party.
Don't set up a host for
campaigns.example.com in the same subnet of your regular smtp gateway if you can avoid it.
Leave the third party in control of the whole process of sending the campaigns and its not your problem to resolve blacklisting etc.