E.email - Emails blocked - Spam detected


I don’t know if it’s the good place but I don’t know where to post.

Here is my issue : Everytime I try to create or reply to an email with a lot of recipients, all my emails from my @e.email address sent to @gmail.com mailboxes (sometime also @free.fr) are blocked and I receive a non-delivery message error with this code :
Diagnostic-Code: smtp; 550-5.7.1 [ 11] Our system has detected
that this message is 550-5.7.1 not RFC 5322 compliant: 550-5.7.1 ‘From’
header is missing. 550-5.7.1 To reduce the amount of spam sent to Gmail,
this message has been 550-5.7.1 blocked. Please visit 550-5.7.1
https://support.google.com/mail/?p=RfcMessageNonCompliant 550 5.7.1 and
review RFC 5322 specifications for more information. r6si12659647wmf.104 -

Of course the link doesn’t help at all because there is a From header, it’s my address @e.email. Is there any way to fix this or a workaround ? If I can’t even send emails to multiple recipients I will have to back to my gmail account and I’d rather not !

Thank you

I just sent a mail from my /e/ email account to 3 different gmail accounts - all were delivered. Sent a reply from one of the gmail accounts and it was also received. May be it has something to do with large number of addresses in the To list

Sending one email by one email is working. I had this issue when I tried to send an email or reply to 10 or more contacts.
The last one was a reply sent to 60 recipients, none of gmail users received the email. I had to forward the email to my gmail account and then reply to the 60 contacts, this way no problem.
It also acted the same with only 10 recipients.