Any recommendations for a reliable SMTP Service Provider?

Hello all.

I have been using MiaB for years and love it as many of you already know from my participation here in the Discourse Forum for Mail-in-a-Box. :slight_smile:

One of the biggest headaches of ‘self-hosting’ email is deliver-ability. I have been blessed that my major installs have not had any issues over the years, but when they do occur they can be maddening.

At this time, one of my servers is having issues with deliver-ability to Gmail … but not the usual, “My email went to spam” but instead delivery is hit and miss with 2 specific accounts (so far). I will get a bounce from Gmail immediately saying that my message was blocked as it likely unsolicited email. The messages in question are REPLIES being sent to their users.

A sample header looks like this: (potential personal info redacted)

<>: host[] said:
    550-5.7.1 [111.222.333.444      12] Our system has detected that this message
    is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to
    Gmail, 550-5.7.1 this message has been blocked. Please visit 550-5.7.1 550 5.7.1  for
    more information. a02rc2840453wmh.112 - gsmtp (in reply to end of DATA

The maddening aspect of this is when I contact the correspondent via another email account, sometimes they say, “Oh I got this email from you” … meaning that it was not ever even blocked to begin with!!! WTH!!! But that is hit and miss, so the end result is that I do not know if this server’s outbound email to Gmail is being delivered, or not.

So in that end … I have to ask the community which SMTP services you have used and how have they worked for you? I am most interested in free services, as this host’s outbound email is in the single digits daily. Can anyone offer real world cases? Thanks in advance for any and all replies!

I’ll just add, unrelated to Mail-in-a-Box, I run a service that uses a commercial transactional SMTP provider and a dedicated IP for my service, and even with a commercial service and dedicated IP I am still blocked by one of the major ISPs. So I haven’t found an escape. (Or maybe I need to use a more expensive SMTP provider? I’m not sure.)


I have used for outbound emails for sites. Have never tried it with MIAB.

@JoshData Nice one, thanks for the laugh.

@alento when you run a mail server, you are at the mercy of other ISPs. They can decide what to block or let in and I don’t think this a problem with MIAB. You can face the same issue even if you use an “SMTP provider”.

Yes, yes … I absolutely agree – this post actually has NOTHING to do with MiaB. Other than the fact that we are talking about email in general.

And I think that is what I really wanted to ask in this post … for those who have used SMTP providers, has it totally eliminated the problem, partially eliminated the problem, or had no real noticeable effect?

I would imagine the answer to be it has helped to eliminate the problem, but there are still problems. Or even that other issues have cropped up. I just really want to get a feel from others what their experiences have been.


I have never encountered a case like yours but you can try it and see if it works for you. Maybe someone in the forum has a more helpful answer than me.

Sometimes the issues are more than weird. For once I was getting a “connection lost” from one of major freemail providers (local, outside of US). Couldn’t figure it out for weeks. Everything was OK according their instructions.

After long mailing history with their support, technical support and etc. I got a message that everything is ok by my side but the TLD domain name is wrong. WTF? I had set a main MIAB TLD domain name to .xyz. Just because it was, at the time, the cheapest option. They told me that they had been blocking this whole (!) TLD, because there are many spammers using this TLD. WTF?

I just moved MIAB to some .com TLD and now it works with them flawlessly…

I wonder whether it is even possible to configure mailserver to be OK with all the weirdest rules of every provider.

Add your domain.

The domain has been actively listed on Google’s Postmaster Tools since the beginning. Domain is verified and has been for 2 to 3 years!

It has quotas so I don’t relay everything through it, just undeliverable domains

I have been using MIAB for regular emails for 3 or 4 years now. Regular emails meaning emails you would manually send to someone, not transactional or marketing emails. I’ve had some issues, but I managed to resolve them - major thanks to the community here. My MIAB usage is about 50 emails [in and out] per day split across 5 domains.

For other types of emails I use Mailgun or Postmarkapp’s deliverability is way better but they only allow transactional emails. Issues with Mailgun included delays in email sending [I’m not referring to greylisting when they try to send the email, but the fact that they put some emails on hold]. I wouldn’t consider this as a major issue but some clients freak out when an email arrives 30 minutes late.

Still, I would recommend Mailgun. You might want to give it a go, especially considering their free tier includes 10k emails per month.

It sounds like you’re experiencing deliverability issues with your self-hosted email server when sending to Gmail. Considering best SMTP services, you might explore options like:

  1. Smtpget
  2. Mailgun
  3. iDealSMTP
  4. Sendgrid
  5. Digitalaka™
  6. Amazon SES

All are good and easy to use. but I have used SMTPget and Mailgun, which offer great configurations with high inbox deliverability. It’s more reliable to many users and you can try them.