Hi. If you wamt to skip an smtp relay you could read up on spf, dkim and dmarc on this really good in depth guide: https://hackernoon.com/a-beginners-guide-to-technical-email-marketing-understanding-spf-dkim-and-dmarc-ygcu32te
If you want to use a smtp relay however i would suggest https://www.smtp2go.com/
They have a free plan with up to 1000 email messages per month. You will still need to set up spf, dkim and dmark for your domain name to make sure email messages doesn't get bounced. But smtp2go has a really good guide setting this up and help you with what to enter in the dns depending on what registrar you use.
I use this and find it really good.
Hope you find a good solution.
To be completely honest I've given up on ever trying to get Office 365 SMTP relay working correctly, especially on copiers. SMTP2GO is a great solution for this - very easy to get up and working quickly, and you don't have to do silly things like putting your public IP in your SPF record. Free plan is 1000 emails per month, which might cover you if you're a private school. Otherwise it's only $10/mo for 10,000 emails.
You cannot receive emails on multiple servers with one domain.
You can send from multiple servers though. If you want to use an additional SMTP service with your domain you can.
I use smtp2go for that. For low volumes it is free.
Just configure the DNS instructions they provide along with HEY's and you will be fine.
I've used SMTP2Go before now, not bad and the free account is pretty good in terms of number of emails allowed.
You can setup an account per customer and then just delete it if they leave so you're still not getting rubbish through when they aren't a customer anymore :)
Far better than those big brand solutions is SMTP2GO. Open-ended free tier, well-priced first paid level tier, good support, good control panel UI.
The 2 killer features that make it for me are -
Sender Domains - setup SPF and DKIM per client domain in their control panel.
SMTP Users - setup access details per client, means you don't have to reveal your own access creds in client configs.
So the client’s “free” email service is being used by spammers? What a surprise. L O L.
I use Smtp2go for outgoing email from a legitimate source. Price varies depending on the number of emails & whether you want your own exclusive public facing IP (this stops the spam listings as you are not sharing an IP with other email senders).
Packages start at $10 / month for 10K emails, shared IP. There is a “free” tier for 1000 emails or less/ month but I’m pretty sure you will end up in a similar predicament if you try and stay free.
I was just thinking the other day that I should start implementing Graph as the standard for sending email from scripts and LOB apps. not only is it fully modern it also is a standard HTTP transaction so won't be blocked by many firewalls which by default limit 25 / 465 / 587 outbound.
Also if you're looking for another SMTP relay I heartily reccomend SMTP2Go. They have a free tier which is nice but the paid tear is extremely inexpensive as well. It's great for relaying from embedded servers and the like, supports basic auth with username/password as well as WAN IP authentication and even supports SPF and DKIM. I haven't used it for any bulk sending but I don't doubt it would work fine for that too.
I use Zoho mail to send out email newsletters, but you can (should, really) also use something designed for this exact purpose like SMTP2Go or Mailgun. Both services have a free tier.
Sending out mass newsletters from consumer services like outlook.com or gmail.com (not G-Suite) can get tricky so I'm not surprised you're having spam issues.
I had multiple issues with gmail as an SMTP relay, and finally set up a free account at https://www.smtp2go.com/ and have been quite happy.
When you're setting up the email, don't forget to click on the little link in the lower right corner, I think it's like advanced email settings or something. It's really easy to miss, but that's where you change the 'from' and a few other things.
I know these buggers inside and out, let me know if I can help with anything. I can check one for reference and get you more specifics.