Error sending emails

Hi there,

I am trying to configure email notifications with Exchange as mail server, but it does not work. Notifications and reports (e.g. weekly) are sent, but only with sender name and correct subject. The content of the email is empty.

Each email creates following error:
(552, b’5.3.4 Header size exceeds fixed maximum size’)
Traceback (most recent call last):
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/”, line 441, in send_one
smtpserver.sess.sendmail(email.sender, recipient.recipient, encode(message))
File “/usr/lib/python3.5/”, line 883, in sendmail
raise SMTPDataError(code, resp)
smtplib.SMTPDataError: (552, b’5.3.4 Header size exceeds fixed maximum size’)

Exchange is 2010, ERPNext: v11.1.61 (version-11) and Frappe Framework: v11.1.56 (version-11).

Exchange MaxHeaderSize is for all connectors 256kb, so should be enough.

Any idea? We do not use any attachments. it is just the mail itself.

Thank you very much in advance,