- Free Tier: Up to 10k emails/mo with Mailgun, up to 12k with SendGrid.
- Low Volume: To send 100,000 emails/mo on a shared IP, you'll pay $45 with Mailgun or $20 with SendGrid.
- High Volume: To send 300,000 emails/mo on a dedicated IP, you'll pay $204 with Mailgun or $199 with SendGrid.
- Deliverability: In today's InboxTrail comparison, Mailgun shows 62.5% inboxing, SendGrid shows 97.5%. 
If you need any help with your integration, I'd be happy to put you in touch with the right people on our team. My email's in my profile.
Disclosure: I'm a SendGrid engineer.
- All paid accounts are given unrestricted access to all Mailgun features. Sendgrid feature gates by plan
- Mailgun has no punitive overages, with Sendgrid you’ll pay as high as $1 per 1000 emails for exceeding your plan. https://sendgrid.com/mkt/assets/pdfs/1-16_SendGrid_Compariso...
Disclosure: I work for Mailgun
- We do offer plans without subuser management and whitelabeling. That's so we can be a cost-effective choice for startups and low-volume senders, which I'd argue is a good thing! Pro customers always get every feature we have to offer, including a dedicated IP.
- Overages rarely happen. In the specific case he's describing, it's nearly always going to make sense to pay $10 for 60,000 more emails.
 As reported by https://www.inboxtrail.com/compare
Disclosure: I lead product development for Mailgun.
1. I didn't configure my MX so you don't track delayed (asynchronous) bounces. It should be your responsibility as an email provider to use an appropriate Return-Path so spam complaints/bounces reach back to the client in this situation.
2. I opened ticket #212817 a while ago (September) about how a MITM could capture emails and replay them by injecting duplicate Subject/From/To headers (article here: https://wordtothewise.com/2014/05/dkim-injected-headers/) but this still isn't fixed today :(
That said, we're very happy with the service :), one of the killer features is how easy it is to manage wildcard sub-domains (compared to the pain it is with Mandrill).
On issue #2, Thanks and apologies for the slow response, This ticket slipped under our radar.
To give you a quick answer: we'll look into the approach you described in your blog post as well as RFC 6376. It seems legit but we'll need to do some more testing to ensure that deliverability does not suffer due to changing how we sign messages. If deliverability does suffer, we can always make this something that is an optional security setting that can be toggled, like how you can enable and disable TLS certificate validation now.
Our security engineer will take a look and reach out to you with more details in the ticket.
The only way to avoid this was to get a dedicated IP which is an additional $59 / month.
I'm not sure why Mailgun couldn't detect this themselves, maybe they do now.
Methodology: a mock verification email with properly structured markup, a verification button, and no marketing content, sent to each provider. https://www.inboxtrail.com/compare#how
A startup I used to work at used SendGrid. I have nothing but good things to say about the experience. I liked it better than Mandrill, which I've used more recently.
I don't work for them.