That would be pretty retrograde. Attachments and links are such basic things, if those have to be disabled something really is wrong.

Set up SPF on the domain and you are much less likely to get spam-blocked.

You can also disable the inline image feature in the configuration if needed, but the tradeoff there is you need to click a show images button.

SPF isn't enough, though. I do have SPF on my domain and I still get blocked by spam filters sometimes (and my IP isn't listed on any blacklists that I know of either, nor is there any SMTP banner issues).

A lot of spam filters also focus on domain reputation. Having no reputation is like having a bad reputation sometimes... meaning your emails could still get potentially blocked just because they don't know you can be trusted.

Try a tool like this out https://spamscorechecker.com/

What does it say?

Made a few changes:
- Added text mail template, for forcing word-consistency with the mail template (SpamAssassin)
- Documented additional SPF settings
- Documented about fixing bad return-path addresses
- Documented configuring HELO
- Removed mail.add_x_header in default PHP setting overrides and documented (it triggers a high SpamAssassin score)

Getting rid of HTML emails / links / attachments really shouldn't be needed. They'd have a tiny impact on spam score and a big impact on UX, and extra complexity in our emailing layer.