Can day3 replace Mailgun?

For ordinary product and application email, yes. For inbound routing, address validation, very long retention or dedicated-IP management at scale, no, and those are the cases where Mailgun earns its place.

Is day3 cheaper than Mailgun?

Both meter sends, so compare at your volume. Where teams save is usually by dropping the second tool they were paying for the newsletter half.

Does day3 have an API as good as Mailgun's?

It is narrower on purpose: one POST to send, idempotency keys, per-email status, plus endpoints for contacts, audiences, topics and suppressions. It does not try to cover validation or inbound.

Will my deliverability change?

Authenticate the same sending domain and bring your suppression list first and the move is close to invisible to mailbox providers, because reputation attaches to your domain rather than to the provider. Warm up gradually if you are moving very high volume.

All comparisons

day3 vs. Mailgun

A Mailgun alternative that is not only for engineers.

Mailgun is sending infrastructure: a capable API, deep deliverability tooling, validation and inbound routing, priced by the emails you push through it.

	day3	Mailgun
Pricing model	By emails sent each month	Also by emails sent, with add-ons
Subscriber limits	Unlimited on every plan	Infrastructure, not a list tool
Product scope	Product updates and transactional email, on purpose narrow	Sending infrastructure: API, validation, inbound routing, analytics
Who can send	Anyone on the team, from a composer	Whoever can call the API or drive the templates
Best for	Small teams wanting one tool for both jobs	High-volume senders with engineers to run it
Starting price	$1/mo for 1,000 emails	Free trial volume, then priced by sends

Comparison reflects each product's pricing model and scope, not specific prices, because those change, so always check the latest on Mailgun's own site.

The core difference

Again not a pricing argument, both meter sends. The difference is who can use it. Mailgun assumes an engineer for every send, so the marketing half ends up somewhere else, on a second bill and a second suppression list. day3 puts a composer, audiences, segments and signup forms on top of the same API, so the person writing the changelog does not need to open a terminal.

The same numbers, both ways

A product team sending 20,000 application emails a month and a fortnightly update to 15,000 users.

On day3

$14/mo

50,000 sends a month fits the 50,000-email plan. 15,000 subscribers costs nothing, on this plan or any other.

On Mailgun

Depends

Mailgun meters sends too, so the bills are comparable; the usual difference is the second subscription the marketing half needs alongside it. We don't print their price here, because it changes and a stale figure would be worse than none. Check it on their own site and run these numbers through it.

Why teams move to day3

One tool instead of two

The API and the list layer in the same product, so marketing and transactional share a domain, an allowance and a suppression list.

Non-engineers can send

A composer, audiences and live segments mean the update does not queue behind a deploy.

DNS set up for you

Connect Cloudflare and day3 publishes DKIM, SPF and DMARC itself, then rechecks until the domain verifies.

When Mailgun is the better choice

Stay with Mailgun if you are sending at real volume with engineers who know it, or if you need inbound routing, email validation, long log retention or fine-grained IP control. That is infrastructure work and Mailgun is built for it. day3 is for teams who want to send good email without running a mail platform.

Moving your list across

Five steps, in this order. The first one is the one people skip.

1

Bring your suppression list first

Push the addresses that bounced, complained, or asked never to be mailed again before you import a single contact. Do it in this order and day3 refuses those rows on the way in, which is the guard working rather than an error. Do it after and you have a window where a re-import can mail someone who already left.

2

Import the contacts

If your list lives in a database rather than in Mailgun, export it from there as a CSV with email and the fields your templates merge. If you have been storing recipients in Mailgun's own lists, export those. day3 dedupes on import and refuses anything already suppressed.

3

Carry the opt-outs across as opt-outs

Contacts already marked unsubscribed import with that status and the date they left on, so your new tool honours a decision made in your old one. Nobody gets re-subscribed by a migration.

4

Verify the sending domain

Connect Cloudflare and day3 publishes DKIM, SPF and DMARC for you, then rechecks until the domain verifies. On another DNS host you get the records to paste. Authenticating the domain you already send from is what keeps your reputation intact through the move.

5

Send one real campaign to yourself

A test send goes to addresses you name, through the same pipeline and the same tracking as the real thing. Compare it against your old tool's output before you point the whole list at it.

What doesn't come across

Email validation, inbound routing and message parsing are not things day3 does, and Mailgun's analytics and log retention go deeper. Templates and webhook handlers are rebuilt, not moved. At very high volume, dedicated-IP strategy and the controls around it are Mailgun's territory rather than day3's.

Questions

Can day3 replace Mailgun?: For ordinary product and application email, yes. For inbound routing, address validation, very long retention or dedicated-IP management at scale, no, and those are the cases where Mailgun earns its place.
Is day3 cheaper than Mailgun?: Both meter sends, so compare at your volume. Where teams save is usually by dropping the second tool they were paying for the newsletter half.
Does day3 have an API as good as Mailgun's?: It is narrower on purpose: one POST to send, idempotency keys, per-email status, plus endpoints for contacts, audiences, topics and suppressions. It does not try to cover validation or inbound.
Will my deliverability change?: Authenticate the same sending domain and bring your suppression list first and the move is close to invisible to mailbox providers, because reputation attaches to your domain rather than to the provider. Warm up gradually if you are moving very high volume.