Please help to set up SPF records for "mydomain.com".
I am sending mail from:
1) server where website "mydomain.com" is hosted. IP address 22.214.171.124
2) from Gmail servers (MX records)
3) I am also using third party SMTP server "mail.otherserver.com", IP address 126.96.36.199 (reverse record for 188.8.131.52 is mail.otherserver.com)
I don't want to allow sending mail from any other servers.
Below are 3 different versions for SPF record. Hotmail.com version:
Open SPF version:
v=spf1 a mx ip4:184.108.40.206 mx:alt1.aspmx.l.google.com mx:alt2.aspmx.l.google.com mx:aspmx.l.google.com mx:aspmx2.googlemail.com mx:aspmx3.googlemail.com mx:aspmx4.googlemail.com mx:aspmx5.googlemail.com a:mail.otherserver.com -all
Google's version is the following (for MX servers):
"v=spf1 a mx a:mail.otherdomain.com include:mail.otherserver.com ~all"
v=spf1 include:_spf.google.com ~all
I don't understand the following things:
1. Why Open SPF uses just "mx" for MX records but Hotmail lists all MX records. The same with A record where is used "a" and IP4.
3. Why Google tells to use "_spf.google.com" - none of MX records contain "google.com".
4. Why Hotmail's version is "a:mail.otherserver.com" but Open SPF uses "include:mail.otherserver.com". Where is the difference between "a" and "include".
I am lost. Please help.