Adding email sync to a SaaS product usually means one of two things: you run an IMAP gateway like EmailEngine on your own servers, or you call a hosted API that does the syncing for you. EmailEngine is a solid self-hosted option that turns IMAP and SMTP into a REST and webhook interface. But “self-hosted” means you own the Redis instance, the OAuth app registrations, the connection pool, and the on-call pager when a provider changes behavior at 2 a.m.
This guide compares a self-hosted IMAP gateway with a hosted unified API, covers OAuth, webhooks, and scaling concerns, and is honest about when running your own gateway is the better call.
Self-hosted IMAP gateway vs hosted unified API
Section titled “Self-hosted IMAP gateway vs hosted unified API”A self-hosted IMAP gateway runs on your infrastructure and exposes IMAP and SMTP as REST plus webhooks, so you operate the process, the Redis store, and the OAuth credentials yourself. A hosted unified API moves all of that server-side: you call GET /v3/grants/{grant_id}/messages over HTTPS and reach 6 providers (Google, Microsoft, Yahoo, iCloud, generic IMAP, and Exchange) through one schema, with no process to run.
Both approaches give you a REST surface over IMAP, so the difference is operational. With a self-hosted gateway you control every connection and pay for every server, which is real power and real overhead. With a hosted API you trade that control for not running anything: no Redis to scale, no OAuth client secrets to rotate per provider, no connection pool to babysit. The table compares the work each model actually requires.
| Task | Self-hosted IMAP gateway | Hosted unified API |
|---|---|---|
| Hosting | You run the process plus Redis | None, fully managed |
| Read mail | REST call to your gateway | GET /v3/grants/{grant_id}/messages |
| OAuth apps | Register and rotate per provider | One connector per provider |
| New-mail events | Gateway posts a webhook you host | message.created webhook |
| Providers | Any IMAP host you configure | 6 providers, one schema |
| Scaling | Add servers and Redis capacity | Server-side, no infra |
For a single mailbox or a homelab, a self-hosted gateway is a fine, dependency-light choice. Across thousands of accounts and multiple providers, the hosted API removes the infrastructure you would otherwise own.
How do I add email sync without building IMAP infrastructure?
Section titled “How do I add email sync without building IMAP infrastructure?”Connect each account once, then read mail with a single HTTPS call instead of running IMAP sockets. A hosted email API handles the IMAP session, MIME parsing, and provider quirks behind GET /v3/grants/{grant_id}/messages, so your SaaS never opens a socket. You skip the Redis cluster, the connection pool, and the reconnect logic a self-hosted gateway makes you operate.
The request below lists the 20 most recent messages from a connected account, whether that account is Gmail, Outlook, or generic IMAP. The endpoint returns each message with from, to, subject, and body already decoded, so you parse JSON instead of FETCH responses. One grant_id maps to one mailbox across all 6 supported providers.
curl --request GET \ --url 'https://api.us.nylas.com/v3/grants/<NYLAS_GRANT_ID>/messages?limit=20' \ --header 'Authorization: Bearer <NYLAS_API_KEY>'from nylas import Client
nylas = Client(api_key="<NYLAS_API_KEY>")
messages = nylas.messages.list( "<NYLAS_GRANT_ID>", query_params={"limit": 20},)
for message in messages.data: print(message.subject, message.from_)For a deeper protocol comparison, see IMAP vs the Nylas Email API.
How does IMAP compare to a REST email API for reading messages?
Section titled “How does IMAP compare to a REST email API for reading messages?”IMAP is a stateful, socket-level protocol (RFC 3501) where you open a TCP connection, log in, SELECT a folder, then run FETCH and SEARCH to read one mailbox at a time. A REST email API wraps that in one stateless HTTPS request to GET /v3/grants/{grant_id}/messages and returns parsed JSON, so there is no session to hold open and no MIME to decode by hand.
A self-hosted gateway speaks raw IMAP for you, but it still keeps those stateful sessions alive inside your infrastructure, which means you own UIDVALIDITY changes, idle timeouts, and per-host quirks. Microsoft deprecated basic authentication for all Exchange Online accounts on October 1, 2022, so every modern integration also needs OAuth, not just a username and password. A hosted REST API moves the session management server-side and exposes the same JSON shape across all 6 providers, so one parser covers Gmail, Outlook, and a legacy IMAP host alike.
What is the difference between push and pull email sync?
Section titled “What is the difference between push and pull email sync?”Pull sync polls a mailbox on a timer or holds an IMAP IDLE connection open per account, so you carry the cost of asking “anything new?” repeatedly. Push sync flips that: you subscribe once, and the API posts an event to your endpoint when mail arrives. With a message.created webhook there is no open socket per mailbox and no polling interval to tune.
This gap dominates at scale. IDLE binds one held connection to one mailbox, so watching 10,000 inboxes means 10,000 long-lived sockets your gateway monitors and reconnects whenever a provider drops them. Webhook payloads stay small, capped at a 1 MB maximum payload size, and oversized events arrive truncated with a .truncated suffix on the trigger name rather than failing. A self-hosted gateway can deliver webhooks too, but it generates them by running that connection pool itself. The hosted model deletes the pool. For the full tradeoff, see webhooks vs polling.
How do OAuth and provider auth work across many accounts?
Section titled “How do OAuth and provider auth work across many accounts?”Each provider gets one connector, and users authenticate through a single hosted flow at /v3/connect/auth that returns a grant you store per account. A self-hosted gateway makes you register an OAuth app with Google and Microsoft separately, store the client secrets, and refresh tokens on your own schedule. A hosted API centralizes those app registrations so you manage one connector per provider instead of raw client credentials in your environment.
At scale, token lifecycle is the hidden cost. Google and Microsoft refresh tokens expire or get revoked, and a self-hosted gateway makes re-authentication your job per mailbox. With a hosted layer, the grant abstracts the token: a grant.expired signal tells you when an account needs to reconnect, and one connector covers every user in a tenant once an admin consents. That keeps OAuth out of your codebase even as you pass 10,000 connected accounts.
When should you run a self-hosted IMAP gateway?
Section titled “When should you run a self-hosted IMAP gateway?”Run a self-hosted gateway when data residency, cost control, or full protocol access outweigh the operational load. If compliance forbids mail content leaving your network, or you sync a handful of mailboxes where a single Redis instance and one server are cheaper than per-account API pricing, EmailEngine is genuinely the right tool. You get byte-level IMAP control and your data never leaves your perimeter.
As accounts and providers multiply, the balance tips toward a hosted layer. Two providers over a self-hosted gateway means two OAuth apps, two sets of host quirks, and a connection pool you scale and page on; six means six. A hosted unified API keeps one schema, one auth model, and one webhook stream across all 6 providers, so the next account is a new grant, not new infrastructure. If you only sync a few boxes you control, self-hosting wins on cost and control. Past a few thousand accounts, the servers you avoid running are the reason hosted APIs exist. See sync email across multiple providers for the multi-provider pattern.
What’s next
Section titled “What’s next”- IMAP vs the Nylas Email API for the raw protocol versus REST comparison
- Webhooks vs polling for the push versus pull sync tradeoff in depth
- Sync email across multiple providers to read Gmail, Outlook, and IMAP through one schema
- Getting started with Nylas to create a project, connector, and your first grant