You send from other people's domains without setting up DKIM/SPF? You're fighting a huge uphill battle if that is the case. I would highly recommend sending from a domain you can verify and then using the reply-to field for responses. It isn't perfect, but your deliverability rates will sky rocket.
We send hundreds of thousands of emails every month. We're by no means a high volume sender, but we've learned a lot dealing with a bunch of these email providers.
Years ago we started with AWS SES. The pricing was amazing but there was no useful customer service outlet. If you were sending via a blacklisted IP it could be weeks before you we're seeing inboxes reliability again. It wasn't uncommon for us to devote 20+ man hours per week in dealing with email issues while using AWS.
Next we moved to MailGun. This was a HUGE improvement, however we were having to request to be moved to 'non-blacklisted' ip's on a regular basis. The pricing was great, but we were still having to invest too many hours dealing with email problems. Mostly fielding 'here is why your emails went to the spam filter, or why they never showed up' questions from our customers. You shouldn't need a template explaining to your customers why emails are showing up in spam boxes!
To be fair, MailGun was fairly new at this point but they were VERY responsive. IP's that had been blacklisted did not stay that way for long.
Lastly we moved to PostmarkApp. They were by far the most expensive ($1.50 per 1000 emails) but I only now even think of emails maybe once or twice per month. Emails just get through, no spam lists, no outages, no carrier blocks, it's amazing. Also, if you do send with enough volume you can drastically reduce the price. I believe we pay about $0.25 per thousand emails now that we purchase 5 million at a time.
They could triple their price and I would eat the costs.
> We send hundreds of thousands of emails every month
With that volume, wouldn't a dedicated Mailgun IP have been worthwhile? You've got enough mail to gain reputation on it, and the flat fee + lower per-email charges could match or be cheaper than Postmark.
Long-time Mailgun user here, but not affiliated with anyone either.
Probably not, there are benefits to shared IP Space, in that you can absorb some complaint/spamtrap issues by piggybacking off others reputation. Its almost like Herd Immunity.
It may very well be something to try out! I think if we ever have issues with our current setup in the future, this is likely what we'll try next. I really liked MailGun's staff by the way! Raquel, James and Matt were absolute godsends on multiple occasions!
For now though we couldn't possibly be happier and would gladly continue using Postmark even if they dropped the bulk discount rates.
We are happy Postmark customers also, sending a couple thousand transactional emails per day.
Postmark delivery rates are of the highest rates I've seen. I also appreciate how easy is to diagnose any delivery problems via their
API or the web interface. In the rare occasions we've needed further details their support staff were immediately helpful.
It is the most expensive service if you don't buy in bulk, but is well worth if you want to stop worrying on blacklists and other delivery problems.
Don't forget to setup DKIM, SPF, PTR Records, etc!