Mailchimp is whitelisted but emails still not forwarded

I would like to use our club email address as the "from" address in our Mailchimp campaigns.

This is problematic as it is likely to cause emails from Mailchimp to be flagged by security software. (stated from does not match actual from)

Mailchimp verifies the domain through email confirmation. It's this verification I can't complete because FreeToastHost is blocking the emails from Mailchimp. It is quite standard for email marketing platforms to allow the user to verify a "from" email through email confirmation.

Here is the full article, including recommending the mail server (FreeToastHost) whitelists the IPs:
mailchimp.com/help/verify-a-domain/

All I'm trying to do is make sure emails FROM Mailchimp TO our club email aliases are not blocked, which they currently appear to be despite being on the whitelist.

Mailchimp is the most popular email marketing platform, so I imagine this would open up the opportunity for lots of clubs (and perhaps districts) to use these modern tools to engage guests/members!

198.2.128.0/18 was blocked for spamming FTH repeatedly
I have removed the block but the addresses maybe blocked again at anytime.

Thank you. I guess like Gmail, Yahoo, or any other large service with thousands/millions of users under the same email domain, you would expect lots of spam from any of these.

I wonder then if FTH shouldn't block the entire IP address but rather the individual emails worthy of being blocked. I presume that's the purpose of the crowdsourced black list?

Depends on the kind of spam. We will take what ever steps we need to protect our server and our members.

Now we're having issues using our custom email addresses.

I can send to officers-8045@toastmastersclubs.org.

But I cannot send to officers@talkituptoastmasters.org.

I think the DNS records are incorrect, but I can't seem to add the required MX record (based on FTH documentation), because Google Domains says "Record already in use."

I'm trying to use:
Name: @
Type: MX
Data: 10 mail.talkituptoastmasters.org

A lookup shows these MX settings:
Type Pref Domain Name Hostname TTL
MX 5 talkituptoastmasters.org gmr-smtp-in.l.google.com 3599
MX 10 talkituptoastmasters.org alt1.gmr-smtp-in.l.google.com 3599
MX 20 talkituptoastmasters.org alt2.gmr-smtp-in.l.google.com 3599
MX 30 talkituptoastmasters.org alt3.gmr-smtp-in.l.google.com 3599
MX 40 talkituptoastmasters.org alt4.gmr-smtp-in.l.google.com 3599

What am I doing wrong here? Thanks for your help.