In https://mxtoolbox.com -> domain health test, we have this issue:


     SMTP Banner Check

    What you see when your domain has this problem

    LISTED SMTP Banner Check

    About SMTP Banner Check

    The SMTP banner issued by your email server did not contain the hostname we resolved for your server’s IP address.

    Additional Information

    Email servers answer connections on port 25 with a string of text called an SMTP Banner whose purpose is to announce the server and any information that the administrator would like to convey to the world.

    It is best practice to put the name of your server in your SMTP banner so that anybody who connects via your IP Address has a clue as to who they are talking to. You will get this warning if the name you present yourself as is not in the same domain as the hostname we get when we perform a PTR lookup on your IP Address.

    For a time many servers would "mask" their SMTP banners by replacing the characters with asterisks to anybody outside of their network. The logic behind this was often that you did not want to broadcast any information about your network to people outside for fear of giving them any information that might help them in an attack against your server. The benefits of doing this are minimal and many servers perform a banner check as part of spam mitigation, so it has a negative cost associated with the practice. Our tool will issue a warning if your banner is masked.

    Some receiving mail servers may use a mismatched or masked banner as an indication of a possible spam source in a scoring system, but most will not reject incoming mail solely on this basis.

    If you do not have a PTR record, or your record does not match your hostname, we recommend that you contact your ISP and ask them to setup a reverse (PTR) record that matches the hostname of your mail server.

even though we've got DNS set as recommended in this thread.

What needs to be done?

  • So your email is done via Google, with your domain's MX records pointing to Google and they handling all the inbound and outbound email? Or there is a difference with your setup compared to that thread? – Keith Langmead Aug 2 '18 at 11:39
  • yes, Google GSuite, and MX correct, here is dig output: id 8318 opcode QUERY rcode NOERROR flags QR RD RA ;QUESTION luzanky.cz. IN MX ;ANSWER luzanky.cz. 359 IN MX 5 alt1.aspmx.l.google.com. luzanky.cz. 359 IN MX 5 alt2.aspmx.l.google.com. luzanky.cz. 359 IN MX 10 alt4.aspmx.l.google.com. luzanky.cz. 359 IN MX 10 alt3.aspmx.l.google.com. luzanky.cz. 359 IN MX 1 aspmx.l.google.com. ;AUTHORITY ;ADDITIONAL – crysman Aug 3 '18 at 8:29
  • In which case mxtoolbox is presumably referring to Google's mail servers having a banner which doesn't match the reverse DNS PTR record for Google's IP address(s) which point to them. In which case I don't think there's anything you can do directly since you don't have control of either setting, so at best it would be a question to pose Google support as any changes would be at their end. – Keith Langmead Aug 3 '18 at 10:47
  • OK, it!s there to solve (possibly?): productforums.google.com/forum/?utm_medium=email#!msg/apps/… – crysman Aug 6 '18 at 12:14

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