Outlook to Gmail emails are bouncing back

So, I picked up a new laptop and got Microsoft Office 2016 installed—everything seemed fine initially:
But whenever I try to send an email from Outlook (using my AT&T account) to a Gmail address, it just bounces back.
This is what I get:

Mail Returned

This is the mail system at host verizon.net.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system

<********@gmail.com>: host gmail-smtp-in.l.google.com[142.250.27.27] said:
550-5.7.26 This message does not have authentication information or fails
to 550-5.7.26 pass authentication checks. To best protect our users from
spam, the 550-5.7.26 message has been blocked. Please visit 550-5.7.26
https://support.google.com/mail/answ...authentication for more 550
5.7.26 information. g10-20020a056402090a00b00423e3538ee2si1518821edz.335 -
gsmtp (in reply to end of DATA command)

Reporting-MTA: dns; verizon.net
X-Postfix-Queue-ID: 7E83B60035
X-Postfix-Sender: rfc822; *****.******@att.com
Arrival-Date: Wed, 18 May 2022 07:07:34 +0200 (CEST)

Final-Recipient: rfc822; *******@gmail.com
Original-Recipient: rfc822;*******@gmail.com
Action: failed
Status: 5.7.26
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.26 This message does not have authentication
information or fails to 550-5.7.26 pass authentication checks. To best
protect our users from spam, the 550-5.7.26 message has been blocked.
Please visit 550-5.7.26
https://support.google.com/mail/answ...authentication for more 550
5.7.26 information. g10-20020a056402090a00b00423e3538ee2si1518821edz.335 -
gsmtp
Mail Returned

This is the mail system at host verizon.net.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system

<********@gmail.com>: host gmail-smtp-in.l.google.com[142.250.27.27] said:
550-5.7.26 This message does not have authentication information or fails
to 550-5.7.26 pass authentication checks. To best protect our users from
spam, the 550-5.7.26 message has been blocked. Please visit 550-5.7.26
https://support.google.com/mail/answ...authentication for more 550
5.7.26 information. g10-20020a056402090a00b00423e3538ee2si1518821edz.335 -
gsmtp (in reply to end of DATA command)

Reporting-MTA: dns; verizon.net
X-Postfix-Queue-ID: 7E83B60035
X-Postfix-Sender: rfc822; *****.******@att.com
Arrival-Date: Wed, 18 May 2022 07:07:34 +0200 (CEST)

Final-Recipient: rfc822; *******@gmail.com
Original-Recipient: rfc822;*******@gmail.com
Action: failed
Status: 5.7.26
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.26 This message does not have authentication
information or fails to 550-5.7.26 pass authentication checks. To best
protect our users from spam, the 550-5.7.26 message has been blocked.
Please visit 550-5.7.26
https://support.google.com/mail/answ...authentication for more 550
5.7.26 information. g10-20020a056402090a00b00423e3538ee2si1518821edz.335 -
gsmtp

Had this happen on my other laptop once—I clicked something, fixed it, and honestly can't remember what.
I went ahead and enabled IMAP in Gmail like it suggested, but still nothing.
If anyone knows what’s going on, I’d appreciate the help—this is driving me nuts.
LP