selfhosted email server, AT HOME with residential IP

I do it. I have a cheap vps that is a smart relay. I use ASSP on the back end VPN to my home.

Yes you can do it but from what I hear without being a big company your chances of not being blacklisted are high. I wouldn't bother personally.

I'll preface this by saying I host my own email, but I don't host it at home. I've also entertained the idea of running a tunnel to bring it in house (although not with cloudflare). You're going to run into 2 main issues that I see:

1. I only did a brief search so I don't know if there's documentation narrowing the range of ips that are used for tunnels, but cloudflare publishes this list of IP ranges that they own. By my calculation that's a little over 1.5M addresses and you don't have any control over what IP is being used when sending out email. This means that you have to add every one of those ranges to your spf record. It also means that if one of those IP addresses does land on a blacklist you have no control over whether or not outgoing mail will be sent from it, and for 1.5M addresses that's a pretty substantial risk.
2. I don't know how you plan on using email, but for me email needs to be reliable. I can't have emails I send getting dropped and I always need to be able to receive email. This is one service that, essentially, there's no maintenance windows on. It has to always be up. That is something that's extremely difficult to do at home. At a bare minimum your risk profile is just your ISP provider. Residential connections generally don't have SLA agreements. This means that if they it's going to go down for an hour or two for maintenance that's outside of your control. Or if there's a storm that takes down the utility lines, there's no guarantees in place about how quickly that can get fixed. And again that's the bare minimum: you also have to think about always having power, hardware failure, software failure, software upgrades, etc. There's a lot that goes into making a service have a high degree of reliability and the reality is that it's exceptionally hard to do at home.

As u/apperrault said though, technically this is probably possible to do.

I don't think so. (I've asked about this on Cloudflare's forum in the past.) You can host a mail server at home, but not through a Cloudflare tunnel. A domain's MX record for its mail server must point to an A or AAAA record, but a Cloudflare tunnel can only be specified using a CNAME record.

Thanks all :) much appreciated

I do too. Axigen mail server and sendinblue now brevity as free smarthost. Mainly use it for notifications from homelab and for things that don't play as well with other free smtp such as the printer I use for scanning and emailing stuff

I would say no. Most ISPs block incoming mail port (25) to residential IPs. Test your ports before everything else.

can I host a mail server on my home server and use cloudflare tunnel.

No. IPs of cloud flare are blocked on most email servers and you really need port 25 be opened. Also residential IPs are in PBL lists, which also used on email servers to get rid of army infected PC. If you going to get intermediate proxy, choose them carefully due to a lot of cheap (or with bad reputation) hostings are rejected (or has much more spam score) too

can you host an email server at home: yes nothing is stopping you.

the question you meant to ask: will it send and receive email with providers like gmail, M365 etc.

the answer to that question: no.

The reputation problem with hosting email at home is that most residential IPs are blacklisted.

The way around this is to relay your mail through another server (all SMTP servers support this, it's often called a "smarthost"). This can either be an SMTP server you setup on a VPS with a clean IP or a commercial SMTP relay like Amazon SES. Cloudflare tunnels are for inbound traffic and can't help with this.

Delivering email to a home SMTP server doesn't have any reputation challenges, you just need to expose port 25 on your SMTP server to the internet (or again proxy it somehow).

Possible - yes.

Do you want it? Probably, no. Especially, SMTP. Better use something like Zeptomail (cheapest) for delivery.

You can still self-host the receiver.

Mandatory do-not-self-host-at-home notice: custom domain at skiff.com is free, iCloud+ Mail is $0.99 and Zoho is $1.25/mo.

Currently that's not possible unless you have business internet.

Basically ISP can mark whole IP ranges as residential, so any email sent from those is marked as spam no matter how you set it up...

It's cheaper to pay Google or similar $6 per month and avoid the hassle of locally hosted mail server.