Why my postfix outgoing mail doesn't go to spam in gmail but it goes to spam folder in yahoo & hotmail?

@ganiszulfa

Do you have a valid PTR (Reverse DNS) record?

PTR records are created for your Droplet during deployment, though can be modified by changing the name of your Droplet post-deployment.

For example, if you deployed a Droplet named mail, the PTR record is not valid. If you named your Droplet mail.yourdomain.ext, a FQDN/FQHN, your PTR record will be valid. This is the only way to setup a PTR record with DigitalOcean for the time being and the documentation doesn’t actually put this out there.

The same applies for any Droplet, whether it’s a web/database server, proxy server, etc. You can set a valid PTR record by just changing the name of the Dropet.

Valid Droplet Name Examples

web01.domain.ext
db01.domain.ext
mail.domain.ext
mx.domain.ext

Invalid Droplet Name Examples

web01
db01
mail
mx

Where domain.ext is your domain (ext = extension – .com, .net, etc).

Once the PTR is set, make sure you’ve set the hostname to match from the CLI using hostname.

i.e.

hostname mail.domain.ext

Where mail.domain.ext is the same as the [new] name of your Droplet (as per my examples).

Even though for web, database, proxy, and similar servers, a valid PTR may not do much, when it comes to mail servers, it needs to be valid.

About the only time I don’t bother is when setting up a VPN.

There’s no clear answer, since they would never directly tell about their spam-filters.

Is it a new domain? Have you sent a lot of emails over the past three months (define a lot)? And to the Yahoo/Microsoft domains?