You can host multiple domains on any mailserver you want. You can assign single or multiple IP addresses to your mailserver, but condition is:
1. your IP address should be clean and reputated which you use for mailing. It should not be black-listed in various RBL's
2. You should use multiple MX records. It would be good is you use your mx records as mail.abc.xom or smtp.abc.com.
3. You must add proper SPF records to every domain hosted with you.
4. DKIM and DMARC records must be updated for every domain hosted.
5. Rdns and PTR records should be done.
6. outlook and yahoo have some certain number of range of mails which will be delivered in inbox everyday from every IP address, if you exceed that number of range your mail will be send to spam. So use of multiple IP addresses is required if you want to mail alot at outlook.com on daily basis.
You can use one PTR record for multiple domains (you can even use one IP address for PTR), there is no issues with that.