How to create a SPF File and where

Hi all,
We are getting complaints that alot of our emails coming from your email server is going to our customer’s spam filter and they never get the emails.

I was told to create a SPF file, but am finding it very hard to set up. Looked for an example to figure out the logic, but am not getting it.

We are using Postfix 2.2 as our mail server with a bunch of domains being controlled by the software. We are also going through our service provider, which is comcast.

Does someone know how I need to do this?

Thanks in advance.

You will have to create the spf record in your DNS zone editor. You will have to create the Record Name as @ Type as TXT and add the data as v=spf1 a mx ~all.

Okay. And that is the problem. I do not know how to do what you are saying. Is there a tutorial or something that shows you how to do this? Very new to all this and am learning as I go.