# Multiple Sending Servers in AcelleMail — Add, Mix, Route

> Spread your volume across several SMTP and API senders for failover, reputation isolation, and headroom past any single vendor's cap. This guide walks the real screens: the type picker, the connect form, the per-campaign "Use all servers" toggle, and the admin pool view.

- Canonical URL: https://acellesend.com/kb/articles/configuring-multiple-sending-servers
- Author: Lena Hart, Email Deliverability Editor
- Category: Sending & Deliverability — SMTP setup, bounce handling, sender reputation, IP warmup, throttling
- Content type: tutorial · Difficulty: intermediate
- Tags: Acellemail
- Published: 2026-03-10 · Last updated: 2026-08-15
- Reading time: 7 min
- Publisher: AcelleMail Knowledge Base, https://acellesend.com/kb

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## Why more than one sending server

A single sending server is a single point of failure: one vendor outage halts your campaigns, one reputation hit poisons everything you send. Running 2-4 servers from different vendors buys you breathing room. Concrete reasons:

| Goal | What multi-server gives you |
|---|---|
| **Survive a vendor outage** | When one server is paused or rejected, the rest of the pool keeps sending. |
| **Isolate marketing from transactional** | Put marketing on one server and one-off/notification mail on another, so a blocked marketing IP can't drag everything else down. |
| **Grow past a per-vendor cap** | New SES and similar accounts start with a low daily ceiling. Add a second vendor and your combined headroom goes up immediately. |
| **Build reputation in parallel** | Warm a new vendor's IPs at low volume while an established server carries the bulk of the load. |

## Add a second server (customer side)

### Open the Sending servers screen

In the sidebar, go to **Sending → Sending servers**. The page is titled **Sending Servers** with the subtitle *"Manage SMTP and API servers that power your email delivery."* Your current servers show in the table, with a search box and **Active / Inactive** + type filters above it.

![Customer sending-server list](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/01-customer-server-list.png)

The right rail shows your vendor mix, total hourly throughput, and warmup status at a glance — a quick way to see how concentrated your sending is on a single vendor.

> The green **Add server** button only appears if your plan allows you to run your own sending servers. On a plan where the administrator manages the pool for you, you won't see it — skip to *Choosing which server a campaign uses* below.

### Click "Add server" → pick a type

The top-right **Add server** button opens the type picker, titled **Choose a server type**. It's a card grid of every provider this install supports — generic SMTP, Amazon SES (API or SMTP), SendGrid, Mailgun, SparkPost, Elastic Email, Sendmail, Gmail OAuth, and any provider added by a plugin (those appear in a separate section).

![Sending-server type picker — "Choose a server type"](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/06-type-selector.png)

Click the provider and integration type you want. The connect form opens with fields specific to that type.

### Fill in the connection and save

For generic **SMTP**, the form (**Connect sending server** → *Connection settings*) asks for host, port (defaults to 587), encryption (TLS / SSL / None), username, and password:

![SMTP connect form](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/07-create-form-smtp.png)

Pick an **API** type instead and the fields change to match. Amazon SES (API), for example, asks for an AWS access key ID, AWS secret access key, and an AWS region:

![Amazon SES API connect form](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/12-create-form-amazon-api.png)

Click **Add server**. AcelleMail saves the credentials and drops you on the new server's detail page. The server isn't probed automatically on save — you confirm it works in the next step.

### Test the connection

On the server detail page, use **Test connection**. AcelleMail tries to connect with the credentials you entered and reports back inline — *"Connection successful."* or *"Connection failed."* There's also a test-send option to push a single message through and check your own inbox (*"Test email sent — check your inbox."*).

![Server test modal](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/05-server-test-modal.png)

If the test fails, click into the server, fix the host / port / credentials, save, and test again. A server stays **Inactive** until you've got a clean connection and enabled it.

## Choosing which server a campaign uses

By default a campaign uses **all** of the sending servers available to you, picked at random per message — that's the redundancy you want most of the time. You control this per campaign in the **Sending servers** section of the campaign setup step (under *Show advanced settings*).

- The **Use all servers randomly** toggle is ON by default. Leave it on and every message goes through a random pick from your whole pool.
- Turn it OFF to **narrow** the campaign to specific servers. Flip the include switch on the servers you want this campaign to use.
- With a narrowed selection, **Adjust weights** lets you set how much traffic each chosen server carries relative to the others (drag a slider per server).

This is how you get deterministic-ish routing without leaving the app: a "newsletter" campaign narrowed to your bulk vendor, a "receipt confirmation" campaign narrowed to a clean transactional server. If every server you picked happens to be inactive at send time, AcelleMail stops the campaign with an error rather than silently falling back to the full pool — so a narrow always means what you said.

> On a plan where the administrator manages the pool, this section is read-only: it lists the servers your plan grants and tells you they're shared and picked at random per message. You can't narrow it from the campaign — that's an admin-side decision (see below).

## The admin pool view (self-hosted operators)

If you run a multi-tenant install, **Admin → Sending Servers** is the full pool across all customers. The top of the page shows three stat cards — **Total**, **Active**, and **Inactive** — over a searchable, filterable table of every server.

![Admin pool — sending-server list](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/08-admin-pool-list.png)

The admin-side server detail has more knobs than the customer one — connection, configuration (including the sending limit), identity / DKIM, warmup strategy, and bounce/feedback handling:

![Admin server detail](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/09-admin-server-detail.png)

To decide which customers can send through which servers, attach servers to plans under **Admin → Plans → [plan] → Sending servers**. Customers on that plan then send through the servers their plan grants — that's how you give a higher tier premium sending IPs while a basic tier shares a default pool.

## Common UI signals and fixes

| What you see | What to do |
|---|---|
| New server stays **Inactive** | Open the server → **Test connection**. Fix host / port / credentials based on the failure message, save, and test again. |
| **Add server** button is missing | Your plan doesn't allow your own servers (or you've hit your server quota). The pool is managed for you under your plan. |
| A campaign sent through a server you didn't expect | With **Use all servers randomly** on, picks are random per message. Turn it off in the campaign's **Sending servers** section and select only the servers you want. |
| Customer says they only see one server | The other server isn't attached to their plan. Go to **Admin → Plans → [plan] → Sending servers** and add it. |
| Campaign won't send at all | Either the customer's plan grants no active servers, or you narrowed the campaign to servers that are now all inactive. Re-check the plan's attached servers and each server's status. |

## What to do after

- Run **Test connection** on every new server before you point a real campaign at it.
- If you added a brand-new vendor or IP, start it at low volume — see [IP warmup schedule for new sending servers](https://acellesend.com/kb/articles/multi-server-rotation-pattern).
- Watch bounce and complaint rates after the first send from a new server — see the related article below.

## Related articles

- [Sender reputation monitoring](https://acellesend.com/kb/articles/sender-reputation-monitoring)
- [Multi-server rotation pattern](https://acellesend.com/kb/articles/multi-server-rotation-pattern)
- [Configuring Amazon SES with AcelleMail](https://acellesend.com/kb/articles/configuring-amazon-ses-with-acellemail)
- [Deliverability incident runbook](https://acellesend.com/kb/articles/deliverability-incident-runbook)

---

## Related articles

- [Feedback Loops (FBL) — Setup + Wire in AcelleMail](https://acellesend.com/kb/articles/feedback-loops-fbl-setup): When a recipient clicks "Mark as Spam" on a Microsoft / Yahoo / AOL / Comcast mailbox, those ISPs send you the complaint via Feedback Loop. AcelleMail processes it automatically — unsubscribes the complainer, updates the complaint stats. This guide walks the setup.
- [How to Set Up Amazon SES with AcelleMail](https://acellesend.com/kb/articles/configuring-amazon-ses-with-acellemail): Create an IAM user and access key in AWS, connect Amazon SES to AcelleMail, share your verified domains with users, and let them verify their own.
- [Amazon SES Sending Limits — Cookbook for AcelleMail Operators](https://acellesend.com/kb/articles/ses-sending-limits-cookbook): SES starts at 200/day sandbox, scales to 50k+/day in production, $0.10 per 1,000 emails. This guide is the practical cookbook: how to grow from sandbox to scale, region-by-region orchestration, what AcelleMail does at each tier.
- [Hard Bounce vs Soft Bounce — Reading the Bounce Log](https://acellesend.com/kb/articles/understanding-email-bounce-types): A hard bounce is permanent; a soft bounce is temporary. AcelleMail records them in the campaign bounce log and treats them differently — hard bounces blacklist the address, soft bounces are left alone for the receiving server to retry. This guide walks the bounce log, the DSN codes, and what each type means for your list.
- [IP Warmup Schedule — Ramping a New Sending Server in AcelleMail](https://acellesend.com/kb/articles/ip-warmup-schedule-for-new-sending-servers): A fresh sending IP has zero reputation. Send 50,000 emails on day one and every major mailbox provider routes you to spam. AcelleMail's Warmup Strategies grow your volume gradually using one of three presets. This guide walks the admin UI plus a realistic ramp plan.