There are 4 types of DNS entries that need to be done for each customer:
Entries related to the use of a dedicated IP address.
3 DNS entries (A, MX and TXT) all related to the same domain name starting with "mta" (example: mta1.yourcompany.ru).
Each additional IP address requires another set of A/MX/TXT and the domain names will be labeled in sequence (example: mta2.yourcompany.ru).
Even if you'll use several domain names, this does NOT generate any extra DNS entries of this type.
We usually select the "main" domain name for the account and append "mta-something" to it.
Entries related to the use of DKIM.
2 TXT entries, with domain names beginning with "_domainkey" and "ofsys._domainkey" (example: _domainkey.yourcompany.ru and ofsys._domainkey.sapato.ru). Sometimes the prefix "ofsys2" will be used when a new key needs to be put in place while preserving the previous one. These 2 entries will exist for every ROOT domain that will be used in the sender field of outgoing messages. (example: yourcompany.ru / yourcompany2.ru, but NOT yourcompany.ru / news.yourcompany.ru since those have the same root domain).
Entries related to the use of SPF.
1 TXT entry with a value beginning with "v=spf1" for each domain AND SUBDOMAIN that will be used in the sender field of outgoing messages (example: yourcompany.ru / news.yourcompany.ru / info.yourcompany.ru).
Entries related to the custom tracker:
1 CNAME entry.
"links.yourcompany.ru --> CNAME --> Ofsys.com"
So in short: 3 entries per IP address, 2 entries per DKIM root domain, 1 entry per SPF domain/subdomain and 1 for the custom tracker.