Web, domains and email
MX
Abbreviation for Mail Exchange
In short and in plain language
An MX record is an entry for a domain in the system of domain names.
It says which server takes in email for the domain.
Without a suitable record, mail sent to your address does not arrive.
So when you change provider, the record is switched over with care.
Definition
An MX record is an entry in the Domain Name System that states which server accepts email for a domain. Without a suitable record, mail sent to your own address does not arrive. When changing provider, this record is therefore switched over with care.