How to link an email server with a customer domain

You should add a few DNS entries to the cloudflare domain. These entries are different based on the registrar (listed below).

1) Go on Cloudflare and then find the customer account:

2) Choose the correct domain then click on "DNS"

3) Make sure there is no other MX entries.

You must check that there is no existing MX entries on the DNS settings.

4) Add the correct DNS entires

Look up for the domain provider and add the correct entries to cloudflare.

eg for infomaniak: 

Infomaniak DNS entries:

MX record

IN  MX  mta-gw.infomaniak.ch.

TXT record

IN  TXT  v=spf1 include:spf.infomaniak.ch ?all

Gandi DNS entries:

MX record

MX @ fb.mail.gandi.net. auto 50

MX @ spool.mail.gandi.net. 10

TXT record

@        v=spf1 include:sendgrid.net include:helpscoutemail.com include:_mailcust.gandi.net ~all

Google Workspace / domains DNS entries:

https://support.google.com/a/answer/174125?hl=en