Multiple Sending Servers in AcelleMail — Add, Mix, Route

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. Most production setups run 2-4 servers from different vendors. Concrete reasons:

Add a second server (customer-side)#

Open the Sending servers screen#

In AcelleMail's sidebar, click Sending → Sending servers. Your current setup shows in the list:

Click "Add server" → pick the type#

Top-right Add server button opens the type selector. Card-grid of every vendor AcelleMail supports — SMTP (any vendor), Amazon SES, SendGrid API, Mailgun API, Postmark, Mailchannels, plus more:

Pick the vendor + integration type. The create form opens with vendor-specific fields. SMTP form (universal pattern — host + port + credentials):

For an API-typed server like Amazon SES, the form changes to vendor-specific fields (Access Key ID + Secret + region):

Fill credentials + save#

For SMTP: host + port + encryption + username + password. For API-typed servers: API key + region. AcelleMail encrypts and stores; credentials are never returned by the API.

Click Add server — the new server appears in your list with a Testing badge while AcelleMail probes the connection. Within a few seconds it flips to Active (or surfaces the connection error inline).

Verify in the admin pool view (multi-tenant installs)#

Self-hosted operators managing a SaaS install see the full pool at Admin → Sending Servers:

Pool view shows: Total / Active / Inactive cards · server-type breakdown bar · per-server quota usage · which plan(s) the server is attached to. The admin side is where you set the Default server for new customers and assign servers per plan tier.

The admin-side server detail has more knobs — pool-wide bounce handler, FBL handler, warmup strategy, identity (DKIM keys), and per-customer access rules:

Routing — which server sends which campaign#

AcelleMail's default routing: round-robin within the pool the customer's plan grants access to. The campaign builder doesn't ask the user to pick a server; the dispatcher does it at send time based on:

1. Plan-attached servers — only servers attached to the campaign owner's plan are candidates
2. Daily quota remaining — if Server A has hit its daily cap, Server B handles the next batch
3. Per-server warmup state — warming servers get prioritized for low-volume campaigns to grow gradually
4. Round-robin within candidates — even distribution after the above filters

For deterministic routing (e.g. always send marketing through Server A, transactional through Server B), use the admin Sending Plan feature to scope a plan to a specific server. Then attach the right plan to the right customer/automation.

Common UI signals + fixes#

# Create a new SMTP server programmatically
curl -X POST "https://acellemail.com/api/v1/admin/sending-servers" \
  -H "Authorization: Bearer $ADMIN_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "type": "smtp",
    "name": "Cluster B SMTP",
    "host": "smtp-b.example.com",
    "port": 587,
    "encryption": "tls",
    "smtp_username": "...",
    "smtp_password": "...",
    "default_from": "noreply@example.com",
    "sending_limit": 5000,
    "sending_limit_period": "hour"
  }'

curl -X POST "https://acellemail.com/api/v1/admin/plans/{plan_uid}/sending-servers" \
  -H "Authorization: Bearer $ADMIN_TOKEN" \
  -d '{"server_uids": ["uid-1", "uid-2"]}'

Related articles#

• Sender reputation monitoring
• Multi-server rotation pattern
• Configuring Amazon SES with AcelleMail
• Deliverability incident runbook