I'm pretty new to email server configuration, so now I'm trying to make my SPF work well but I'm facing a strange problem. My SPF is like this
v=spf1 +mx +a +ip4:xxx.xxx.xxx.xxx +include:_spf.google.com ~all
so with this we can send emails from our server and people who use Gmail to manage the email account can send too. But we have some people who use other mail client like Thunderbird, Outlook, etc. And when they send an email to someone who uses Gmail, sometimes it goes to Spam because Gmail says that the SPF does not allow that email. So I'll give an example. I use Thunderbird, when I send a message to a Gmail it accept with the log
spf=pass (google.com: domain of myemail@mydomain.com.br designates xxx.xxx.xxx.xxx as permitted sender)
The IP is from our server. And Here (in the same building, so the same IP) another person uses Outlook when send an email to Gmail it returns
Authentication-Results: mx.google.com;
spf=softfail (google.com: domain of transitioning another@mydomain.com.br does not designate yyy.yyy.yyy.yyy as permitted sender) smtp.mailfrom=another@mydomain.com.br
Received-SPF: softfail (google.com: domain of transitioning another@mydomain.com.br does not designate yyy.yyy.yyy.yyy as permitted sender) client-ip=yyy.yyy.yyy.yyy;
So the point is, why is the email from another@mydomain getting our external IP and the myemail@mydomain getting the IP from the server if they are being sent from the same IP?
And how can I get around this, some people who use Outlook work in other places, and their emails go to Spam because SPF does not allow them. SPF apoint another IP, the external IP where the sender is, not the IP server like the myemail@mydomain.
I can put the IPs in the SPF key, but it does not make much sense because the IP can change, so I'll have to change the SPF key a lot of times.
I didn't find some config like the _spf.google.com
for Outlook and Thunderbird...