Calendar Invitations classified as SPAM

[janharms]

Steps to reproduce

1. Invite user (isnotspam.org) to meeting
2. Check spam score

Expected behaviour

Mail should not be classified as spam

Actual behaviour

Mail is classified as spam

Server configuration

Operating system:
Debian 8

Web server:
nginx 1.14

Nextcloud version: (see Nextcloud admin page)
13.0.1

Updated from an older Nextcloud/ownCloud or fresh install:
Updated over the years

Are you using encryption: yes/no
no

Are you using an external user-backend, if yes which one: LDAP/ActiveDirectory/Webdav/...
no

Logs

isnotspam

isnotspam log

* 3.5 BAYES_99 BODY: Bayes spam probability is 99 to 100% [score: 1.0000]
* -0.0 SPF_PASS SPF: sender matches SPF record
* -0.0 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain
* 0.2 BAYES_999 BODY: Bayes spam probability is 99.9 to 100% [score: 1.0000]
* 0.1 HTML_MESSAGE BODY: HTML included in message
* -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain
* 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid
* -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature X-Spam-Status: Yes, hits=3.7 required=-20.0 tests=BAYES_99,BAYES_999, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HTML_MESSAGE,RP_MATCHES_RCVD,SPF_PASS autolearn=no autolearn_force=no version=3.4.0
X-Spam-Score: 3.7

[tflidd]

3.5 BAYES_99 BODY: Bayes spam probability is 99 to 100% [score: 1.0000]

This is a trained filter on your mail server. It means that the invitation from Nextcloud is too close to spam you have received in the past (or the spam used to train your spam filter). Not sure what Nextcloud could do, if the wording of these mails is not great, we could improve it. Except for that, no HTML mails?

In your case, you could train your mail filter with Nextcloud invitations. Or add an exception for mailserver which is sending out the invitations.

[janharms]

I assume editing the invitation template or switching to text only mails could be a solution. As this is the bayes database of isnotspam.org I cannot take influence on this.
Is it possible to edit the tempaltes or switch to text invitations?
Regards

[MorrisJobke]

Is it possible to edit the tempaltes or switch to text invitations?

We added the text-only option to 13.0.2: #9205

[janharms]

Thank you. Great timing.

Edit:
It seems the application of the BAYES_99-Rule is not representative. Other Online-Spam-Checkers do not make use of it. I'll report back when I have confirmation from gmail users if the receive my invitations as ham.