As the title says.

Gmail does not accept any mails from our woocommerce shop since we installed the FPD Plugin and marks them as spam.

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  xxxxxxxxxxxx@gmail.com
    (generated from xxxxxxx@xxxxxxxxx.de)
    host gmail-smtp-in.l.google.com [74.125.133.27]
    SMTP error from remote mail server after end of data:
    552-5.7.0 This message was blocked because its content presents a potential
    552-5.7.0 security issue. Please visit
    552-5.7.0  https://support.google.com/mail/?p=BlockedMessage to review our
    552 5.7.0 message content and attachment content guidelines. p15si3182834wrs.110 - gsmtp

  We tried to get rid of the product thumbnail in the mails but that seems to be not the problem... The Mails still get marked as spam.

What can we do now?

got a similar warning trying to send the JQuery package and add-on packages to our developer's gmail address:

Failed Recipient: xxxxxxxx@gmail.com

Reason: Remote host said: 552 5.7.0 This message was blocked because its content presents a potential

5.7.0 security issue. Please visit

5.7.0  https://support.google.com/mail/?p=BlockedMessage to review our

5.7.0 message content and attachment content guidelines. z23-20020a63ac57000000b003fdd5d89ba0si12633860pgn.228 - gsmtp 

What is causing the issue with the code and how have you resolved it?

Would want clients email orders from our site being blocked by Gmail or other email clients - how have you resolved this?