Notify vs Mailgun: which is simpler if I only need transactional email?

If by Notify you mean Notify.cx, then for your specific use case—“I only need transactional email”—Notify is simpler.

	Notify	Mailgun
Focus	Transactional email only	Full email platform
Basic API	One JSON POST	Multipart/form-data API
SDK required	No — fetch is enough	Official Node SDK available
Auth	Simple API-key header	HTTP Basic auth
Logs	Built in	Built in, with richer event tooling
Webhooks	Yes	Yes
Templates / validation / routing	Minimal	Extensive
Best for	“Just send my app emails”	More complex email infrastructure

Notify's basic send is essentially four fields (to, from, subject, message) plus an API key. Notify+1

Mailgun is perfectly capable, but its API exposes considerably more machinery—templates, events, webhooks, validation, routing, regional endpoints, etc. Its send API uses a more involved form-data request. Mailgun Developer Documentation+1

My recommendation

Pick Notify if:

• You need password resets, verification emails, receipts, alerts, etc.
• You want the smallest possible integration.
• You don't need sophisticated email validation/routing.
• You'd rather not learn a large email platform.

Pick Mailgun if:

• You expect your email requirements to grow.
• You need advanced routing, validation, templates, or detailed event tooling.
• You already use Mailgun elsewhere.
• You care about having a more mature, broad ESP platform. Mailgun+1

So if your requirement really is “my app needs to send transactional emails and nothing more”, I'd choose Notify. It's essentially an email pipe rather than an email platform.

One caveat: Mailgun is the safer choice if you're optimizing for breadth and long-term infrastructure flexibility; Notify is the better choice if you're optimizing for simplicity.