.NET, to SendGrid, to Gmail getting From Header missing

Sending the email to google user is always be a challenge, out of 1000+ factors Gmail mainly consider the sending domain and IP reputation. You have to build a good reputation in front of Gmail. Please be remember for Gmail It doesn't matter whether your sending IP is listed in Spamhaus or any other major DNSBL.

It's all about reputation and to build the reputation you have to send a good email. Google always loves email replies so ask or encourage your users to reply your email.

One thing I have noticed that the IP -176.31.231.235 doesn't seem to be have standard PTR. rDNS for IP 176.31.231.235 ns3481305.ip-176-31-231.eu reference - http://multirbl.valli.org/lookup/176.31.231.235.html

I strongly recommend changing the rDNS of this IP from generic to a specific one. Also, please add Google TXT record in your domain's DNS so that you can be aware of what is happening with your domain and IPs. Google postmaster dashboard also provide other useful metrics. https://postmaster.google.com/

Hope this helps...

Either find a mail provider that helps you achieve compliance with the common terms of such providers - or do work on implementing best practices.

I recommend you use one of the many (often free) third-party test services to confirm that your PTR,TLS,SPF,DKIM,DMARC,unsubscribe-headers,.. is working and additionally use the Google-provided postmaster tools to see the specifics for their servers.

it mostly talks about how to avoid messages being treated as spam, not how to get an IP address unblocked

Google points you to the same list of best practices because they really do expect senders to consider many if not most of them. They mean it when they say they will not just "unblock" you if you request so.

However.. non-spammers may get to effectively lift the block by making it easier for recipients to tell them apart from spammers. Remember that spam filtering at scale tends to be a lot more fine-grained than binary "you're blocked" and "free for all".

You might discover that as soon as FCRDNS & authentication is setup, your mail is no longer rejected blaming "your IP address" but instead evaluated using on a bigger/better aggregate of what Google knows about your ISP, your domain, your sending history and more.

Also, reconsider sender addresses like noreply. If a message is not appropriate to process replies for, it may well not be appropriate to fill peoples inboxes with either.