XF 1.5 XenForo Password/Verification Emails Being Marked as Spam due to content?

I've had multiple users inform me that their gmail (and other email providers) have been flagging the content of xenforo password resets and validations as spam due to being "similar to other spam messages". This is not an issued that we had when we were using vBulletin, so I know our domain has not fallen into some spam blacklists, etc. Does anyone have any advice? Can e-mail templates be changed to simply contain a plain text link and instructions, and nothing else? This is a consistent pain thus far.

What mail server/service are you using for sending your emails?
Perhaps it's based on that?
We have a dedicated mail-server built into our VPS that handles all outgoing forum messages. That hasn't changed since we moved over to XenForo, which is when this problem started.

Is the SPF and DKIM set correctly for the mail server?
Have you run your site through the mxtoolbox?
I'll double check. Like I said before, this wasn't an issue until we switched over to XenForo, and Gmail is specifically saying the contents of the message are the reason they're being flagged as spam.