> A biz that can't deliver to gmail is a terrible smell though.
If anything, it means that teams are probably too independent and that there is no central approval process for things like sending emails.
For example, a lot of companies use products like Greenhouse. I am sure this will send email from your domain on your behalf. If you don't know what you have to talk to the DNS administrators to add a bunch of TXT records to enable that, you will just notice that some percentage of emails never get delivered (or if the product doesn't tell you that they're bouncing, you may never know. how could you?)
If you use something like Zendesk, you'll note how many people have been burned by this. By default, they end up using something like support.yourdomain.com because despite detailed instructions on how to set up the necessary DNS records to send email from youdomain.com, people still fail to do it right and then complain "nobody ever sees my support tickets".
My point is, email has been abused so heavily that it is somewhat difficult to set up a working system. That was my experience when I ran my own email server. Although I did OK with delivery, I also aggressively filtered messages and used greylisting. This broke a lot of broken email systems, whose administrators immediately blamed me. (I had a long back-and-forth with some company that wanted to hire me. Their email system was super broken. They blamed me and said that they weren't interested in a programmer that couldn't set up a mail server. LOL.)