Teams channel received email, shows subject but body is "..." (HTML content)

Question

Hi.
We send html email through smtp server.
Teams channel received the email, shows subject but body is "...".
We can load original mail (View original email).
P.S. Outlook displays the email correctly.

Checked:
https://support.microsoft.com/en-us/office/send-an-email-to-a-channel-in-microsoft-teams-d91db004-d9d7-4a47-82e6-fb1b16dfd51e

Maybe some additional limitations (+ rendering)?