sendmail denies relaying, says "Cannot resolve PTR"

I am trying to migrate my website and mail server to a new VPS at the IP address 65.181.125.58. To test whether receiving mail is set up correctly, I used my third-party server 66.90.104.230 and tried telnetting to 65.181.125.58 port 25 to send mail, but I got the error "Relaying temporarily denied. Cannot resolve PTR record for 66.90.104.230":

(I tried multiple times to post the entire transcript of the conversation with the SMTP server, but linuxforums kept blocking it because of at-signs or hostnames that looked like websites, so I am only able to post the last line of the exchange, but I hope this makes it clear what the problem is):

450 4.4.0 Relaying temporarily denied. Cannot resolve PTR record for 66.90.104.230

The odd thing is that I've found multiple sources claiming that sendmail "by default doesn't deny relaying based on a missing PTR record", e.g.:

objectmix.com/sendmail/211946-cannot-resolve-ptr-record-stopping-relay.html

.experts-exchange.com/Software/Server_Software/Email_Servers/Q_21411329.html

(linuxforums will not let me post those as actual clickable urls because I'm a new user, but you get the idea)

but here that's exactly what sendmail is doing even though I haven't changed any options. How do I get it to stop?

I don't want to set up a PTR record for 66.90.104.230, I want to make sure the new VPS accepts mail from IPs without a PTR record since that's the way the old VPS worked and I can't risk causing any breakages by changing the way mail is handled.

At peacefire.org/sendmail.mc I have posted a copy of my sendmail.mc file. Note in particular the line

FEATURE(`accept_unresolvable_domains')dnl

which made me think I definitely wasn't supposed to get this error.

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