Exchange 2016: How many attachments may be in the email?

Have you ever wondered how many files you may attach to an email?
For Microsoft Exchange 2016 (CU6) is 249 (250 MIME parts). And it is an unchangeable parameter. Not so much, isn't it?

MaxBodyPartsTotal
This limit specifies the maximum number of message parts that can be used in a MIME multipart message. The value is 250.
https://technet.microsoft.com/en-us/library/bb397226(v=exchg.150).aspx

In the RFCs I can't find any mention of maximum number of MIME parts or attachments. Also I found information that in Gmail there is no limitation to number of files attached, only message size (300 files was delivered perfectly). Feel free to correct me if I'm wrong.

Some tests in Exchange

After sending the email with 250 attachments I received the NDR "Delivery has failed to these recipients or groups" without error code, but it can be like that "#554 5.3.4 STOREDRV.Submit; Content conversion limit(s) exceeded ##".

In the source of the email we can see two parts of the message body in "text/plain" and "text/html" (which I guess are defined as one MIME part) and 250 files (application/octet-stream).

The email with 249 attachments was delivered successfully.

Outlook

In the GPO (Office 2013 Administrative Template files) noticed an interesting key "User Configuration/Policies/Administrative Templates/Microsoft Outlook 201*/MIME to MAPI Conversion/Change the limit for the number of MIME body parts".
Link. Description:

"By default, the limit is 250 for the number of MIME body parts when an e-mail message is converted from MIME to MAPI. The number can be set to any positive integer. This helps prevent scenarios in which Outlook hangs while attempting conversion."

Configured (500), checked, but nothing has changed.