Here’s how to fix the Reverse DNS does not match SMTP Banner issue reported by MXToolbox.
First off you need to find out what your SMTP banner is. You can do this by performing the Test Email Server check on MXToolbox. This will tell you what is setting your SMTP banner. It will likely be coming from the email server you are using, or it will be coming from some intermediate source. This intermediate source may be an antispam server hosted by you or a third party.
If the SMTP banner is set by your email server, you need to Google how to set the SMTP banner within that particular type of email server. Same with the antispam server. If however, your SMTP banner is set by a third part service that your email goes through, chances are you can’t fix this. The workaround would be to set up a PTR (Reverse DNS) record at your ISPs side, pointing to the SMTP banner. This may not be advisable as it may then cause your reverse DNS to point to an invalid hostname. So my advice is to either check that the SMTP banner matches the reverse DNS record setting and if not, don’t set it. In this scenario, my advice would be to simply ignore the Reverse DNS Does Not Match SMTP Banner warning from MXToolbox, unless email from your domain is being marked as spam and you’ve done everything else on MXToolbox’s hit list and aren’t on any blacklists. In which case, your only option is to change providers of the gateway service that you are using.