It helps to remember that a 1099-M form is Informational Reporting. By you reporting this to the entity you paid and to the IRS, now the IRS knows to watch for and expect at least this much info from that entity you reported to/on.

And this is a bit backwards or incomplete: "Does anybody know why there is no need to file form 1099 to corporations? Also, why there is no need to file form 1099 to rental real estate as well?"

Box 1 is Rent, no matter the entity type (corporate or LLC or individual), but it relates to whose income this will be. Rent to a Property Manager is being managed on behalf of Owners. That's why a real estate Management company doesn't need to get a 1099-M for Rent in Box 1 from the tenants. But the same tenants would send a 1099-M to your client, if your client is the owner of the units being rented, and manages their own property.

There is no specific rule for Not issuing to Corporations, so much as there are regulations for each box. For instance, you are supposed to report to Law firms and Accountants, for services, and I would guess this is because the IRS doesn't trust them to report accurately and directly. And medical services are reported, yet many law firms, accountants and medical providers have an incorporated entity.

And while Box 1 and 7 have a $600 minimum for triggering reporting, box 2 for Royalties is $10 or more, not $600 or more.

Of course you have been tracking everything. Using QuickBooks or not, doesn't eliminate the need to follow the reporting requirements. Your bookkeeping doesn't substitute for required reporting; you use it for your reporting, and to confirm what is reported to you.

"My client(partnership) sent over a form 1099 MISC he received from a tenant to me."

Their tenant did the right thing, and your client did the right thing.

You want to read the 1099-Misc instructions. And for this new year, 1099-NEC, as well.