The ADSP box on the Virtual Domains screen is something you change yourself.
So you need to apply the policy as you see fit, no matter what is currently set. As long as the Set column is active [*], the ADSP choice you make is applied after you click the
Save Changes button. To test this:
- Go to http://www.appmaildev.com/en/dkim/
- Click Next Step
- In the Fastmail web interface, send a test message from your domain to the address provided at the website I just mentioned.
- You should quickly get a reply email. Look for DKIM result: pass, and the next section will show PublicKey: mesmtp._domainkey.yourdomain.xxx
- The public key you see here should match that shown on the Virtual Domains screen for that domain.
- Then go to https://www.unlocktheinbox.com/dnstools/a/ and enter your domain at the end of the first field, such as _adsp._domainkey.fastmail.fm, then look up the Authoritative (SOA) Server results. Be sure to examine the SPF/TXT record tab at the bottom after the page refreshes, and remember that there may be some caching delays if you make changes.
- The results for fastmail.fm are dkim=unknown, since Fastmail doesn't want to block users who use their Fastmail address but send from other SMTP servers.
- See http://en.wikipedia.org/wiki/Author_...ning_Practices for more details about the three ADSP choices (unknown, all, and discard).
- If you always use the Fastmail SMTP server to send messages from your domains, you should be able to use the discard signing practice. This policy instructs email systems that they are allowed by your domain to silently discard messages which contain an improper or no DKIM encryption signature. This is simply a directive from your domain records - there are few email systems which will discard such messages at this time.
- The all policy indicates that all messages sent from your domain are signed, so email systems might consider messages with a failed or missing DKIM encryption signature to be possible spam.
Bill