I have DKIM, DMARC, and SPF set up on Cloudflare settings, and they all propagate with no problems. I can send emails through webmail from the same domain. However, when I try to send emails through Outlook (desktop), they cannot go out, sitting there and time out. I have other domains on the same server not managed by Cloudflare, and I do not have any issues with them at all. What is the bottleneck?
It’s difficult to say without knowing the domain.
Is the client configured to send using a host name like smtp.example.com? Is the hostname set as DNS Only 
on the Cloudflare dashboard?
Michael,
The domain has mail.example.com with regular ports for IMAP and SMTP. There is nothing different about this domain besides DNS running through Cloudflare. I have other emails from other domains on the same servers, they can send and receive emails with no problems. However, this domain cannot even be set up in Outlook.
?Michael,
the domain name is zinatgroup.com. I ran a test on mail.zinatgroup.com in Cloudflare and the only two things should errors were:
not_found_ds_record: The hostname has no DS records.
slow_ttfb_on_cache: The response was slower than 800ms and the requested resource is cacheable on Cloudflare.
Change the DNS entry for mail.zinatgroup.com to DNS Only 
.
Any DNS entries used for protocols other than HTTP (such as IMAP, SMTP, POP3, FTP etc.) must be .
No, there are no specific ports or protocols configured on the domain and yes Cloudflare is used for DNS on the main domain. I have used Quick MX Auth Tool on rocketscum.net and everything seems to be normal.
I ran a test on SMTP through MXTOOLBOX.com and it timed out after 15 seconds on two different occasions. The IP addresses shown belong to Cloudflare. So, I assume the bottleneck resides in Cloudflare. Now, the question is how to figure out the settings in Cloudflare not to timeout and route the requests?
Connecting to 104.26.1.153
5/2/2022 3:59:11 PM Connection attempt #1 - Unable to connect after 15 seconds. [15.01 sec]
LookupServer 15053ms
Connecting to 172.67.75.197
5/2/2022 3:58:42 PM Connection attempt #1 - Unable to connect after 15 seconds. [15.02 sec]
LookupServer 15024ms
Now, the question is how to figure out the settings in Cloudflare not to timeout and route the requests?
Cloudflare does not forward SMTP - if you want SMTP to be available on a record, you need to set it to DNS only (grey cloud) like Michael mentioned.
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