Can i use mailcow on a dynamic IP with DDNS-updater for my usecase?

I'm in your situation and what I do is relay my email through Amazon SES. It's unlikely to get blacklisted and it's cheap. Costs me literally $0.01/mo to use.

On the inside I have a postfix server all the systems are configured to send through. The postfix server is set to relay all messages to SES. You also need to make sure that SES is configured in your domain SPF record.

EDIT: I just re-read your message. If all you're looking for is outbound email, mailcow is significant overkill. All you need is an MTA like postfix.

I use a wireguard tunnel and port forwarding from a vps to a mailinabox instance serving mail for my various domains. If you have your SPF/DKIM/rDNS set up correctly, it's not too bad with respect to management and mail delivery, plus you don't have to trust anyone with your data. As far as other mail servers are concerned, your VPS IP is the only IP they see. I pay $10/yr for the VPS

Just an FYI, zoho has a free tier with SMTP outgoing and 1 address that would work perfectly for this.

I also have mailcow behind a dynamic in. I wrote a script that updates my cloud flare dns entries as soon as it detects that the ip changed. https://github.com/tinkermesomething/scripts-stuff/blob/main/cloudflare_DNS_updater.sh

I then use online services to check if they’re likely to get marked as spam

IP changes are not your concern. It is likely that your ISP blocks outgoing port 25, you can check with nc gmail-smtp-in.l.google.com 25 and if you don't get any output its blocked. If you don't have very many users on your Pterodactyl server, I would suggest just using a gmail account with SMTP in pterodactyl. If you have port 25 unblocked and want to selfhost email, mailcow is a great option and really easy to set up.

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Given the answers given, I would suggest getting a cheap VPS that's gonna cost you like $5/mo but you know its IP will never change, and you can get the reputation to improve and become good whereas residential IPs are pretty much all blacklisted everywhere as 99% of emails coming from residential IPs is sent out by malware.

Any cheap VPS can handle email just fine on its own but you can also treat it as just an entry and exit of a VPN. So you can technically have your mail locally at home it's just gonna go through that VPS first before reaching your server, same for outgoing.

On incoming side of things:

In between your IP change, your script update your DNS record, and finally sender’s server gets the new IP address, you may lose emails coming to you. Most mail providers will eventually, at their chosen cadence and frequency, attempt to re-deliver the messages, so you might get them eventually on a delay. There is no way of knowing what you’re not missing in the event the sender’s server not retrying. Mails coming to you is delivered into folders per your configuration, and should not end up in spam because of your IP change.

On the outgoing side of things:

Every IP address has some reputation attached to it. Residential addresses tends to score lowly because of people getting virus/malware and become part of a bot net to spam. As you’ve got no control over the IP address you’d receive from your provider, there’s no guarantee if you will receive a clean IP or not. Worst case scenario here is you might end up with a blacklisted IP, and your mail never gets accepted (or silently discarded) by receiver’s mail server. You may also run into SPF record needing the IP address but you can probably get your DDNS script to update this as well or, maybe just use an A record.

If your intention is to receive emails, it might work, but you might miss a message or few.

If your intention is to send mails, it is cheaper and easier to just get a transactional mail provider and pay pennies per thousand mails, and never worry about it.

If your intention is to make a full fledged mail service with send and receive… it’s just not worth the hassle and headache.

You need to create an MX record in the DNS zone of your domain. Something like:

@ IN MX 10 my.zome.
@ IN MX 20 server1.my.zome.

You can create 1 MX record or more. 10 and 20 server priority for input mails.

Then you need to create an spf record. There are several options here. For example

@ IN TXT "v=spf1 +a +mx -all"

allows you to send emails from A domain records, then from MX domain records and prohibits from all other hosts.

Theoretically, you can only create an SPF record with A but without MX and dont create MX DNS records. Although I have not tried this configuration.

This is the minimum set after which you will get into spam, but at least the letters will reach.

You also need to make a PTR record to avoid spam folder, but this is not possible on a dynamic IP.

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