Can mail still be delivered without MX records?

Sometimes, and that is the problem. The historical fallback is for a sender to use the domain's A record, so mail can end up at a web server. The behaviour varies between senders, so the results are inconsistent rather than reliably absent.

A single MX record with priority 0 and a hostname of one dot. It states that the domain accepts no mail, which lets senders fail immediately and clearly instead of retrying for days.

Can an MX record point at an IP address?

No. An MX record must contain a hostname, and that hostname must resolve to an address. Pointing one at an IP is invalid and will be rejected or ignored.

Do I need MX records to send mail?

Not to send, but you do need them to receive, including bounces and replies. A sending-only domain with no MX cannot receive delivery failure notifications, which makes list hygiene and reply handling impossible.

CriticalInfrastructure

No MX records found

The domain publishes no MX records, so no mail server is nominated to receive mail for it. Anything sent to an address at this domain has nowhere to go and will bounce. If the domain is not meant to receive mail, that is a legitimate state, but it should be declared with a null MX record rather than by publishing nothing.

Check your own domainMX lookup

What causes this

MX records tell other mail servers where to deliver mail addressed to your domain. With none published, a sending server falls back to the domain's A record in some implementations and simply fails in others. If this domain is meant to receive mail, this is a total outage.

What it breaks

Mail sent to addresses at this domain is not delivered. Senders receive bounces, and in many cases the bounce is a permanent failure.

What the receiving server does

A sending server about to deliver to your domain queries MX. With no answer, the historical fallback is to try the address in the A record instead, which means mail can be delivered to a web server that is not expecting it, or bounce after a delay while retries are exhausted. Neither outcome is good. Publishing a null MX makes the intent explicit and produces an immediate, honest rejection rather than a slow failure.

Receiving mail, or declaring that you do not

There are two correct configurations here and one incorrect one. Publishing nothing is the incorrect one, because it leaves sending servers to guess.

receive10 mx01.mail.example.net.priority then hostname; lowest number is tried first

receive20 mx02.mail.example.net.a second host for redundancy

no mail0 .null MX: states clearly that this domain accepts no mail

wrong(nothing published)senders fall back to the A record or bounce slowly

How to fix it

Publish the MX records your mailbox provider specifies.

Get the MX hostnames and priorities from your mailbox provider's setup documentation.
Create one MX record per hostname at your root domain, with the priorities exactly as documented.
If this domain is deliberately not used for receiving mail, publish a null MX record instead so senders fail fast and cleanly.

If you send with

Google Workspace: Modern setups use a single MX record pointing at smtp.google.com. Older documentation lists five ASPMX hosts at different priorities; both work, but mixing the two schemes does not. Use one or the other.
Microsoft 365: A single MX record pointing at your tenant's mail.protection.outlook.com host. The hostname is specific to your tenant, so it cannot be copied from another domain's configuration.
A domain that only sends, or does not send at all: Publish a null MX: priority 0 with a single dot as the hostname. Pair it with v=spf1 -all and a DMARC record at p=reject to close the domain off completely. This is the correct configuration for parked domains and for domains used only for outbound relay.

Confirming the fix worked

Decide whether this domain should receive mail at all, and configure for that answer rather than leaving it undefined.
If it should, publish MX records pointing at hostnames, never at IP addresses, which is not valid.
If it should not, publish the null MX record and confirm it is the only MX entry.
Send a test message to an address at the domain and confirm it either arrives or is cleanly rejected, rather than hanging in retry.

Common questions

Can mail still be delivered without MX records?: Sometimes, and that is the problem. The historical fallback is for a sender to use the domain's A record, so mail can end up at a web server. The behaviour varies between senders, so the results are inconsistent rather than reliably absent.
What is a null MX?: A single MX record with priority 0 and a hostname of one dot. It states that the domain accepts no mail, which lets senders fail immediately and clearly instead of retrying for days.
Can an MX record point at an IP address?: No. An MX record must contain a hostname, and that hostname must resolve to an address. Pointing one at an IP is invalid and will be rejected or ignored.
Do I need MX records to send mail?: Not to send, but you do need them to receive, including bounces and replies. A sending-only domain with no MX cannot receive delivery failure notifications, which makes list hygiene and reply handling impossible.