Deliverability

Deliverability is the probability that your email lands in the inbox rather than spam. It is determined by your sender reputation — a score inbox providers maintain based on your bounce rate, complaint rate, engagement, and authentication. This page covers everything you need to maintain a healthy sending reputation.

The numbers that matter

AWS SES monitors your account-level metrics continuously. If either number crosses the threshold, your account is paused for review.

Metric	Warning level	Pause level	Best practice target
Bounce rate	5%	~10%	< 2%
Complaint rate	0.08%	~0.1%	< 0.05%

These are rolling metrics, not monthly averages. A single large campaign with a spike in bounces or complaints can trigger a review even if your historical average is clean.

IP warm-up for new accounts

When you start sending from a new AWS SES account, inbox providers have no reputation data on you. Sending at full volume on day one almost always leads to spam placement. Warm-up solves this by gradually increasing volume so providers can build confidence in your sending patterns.

Recommended 4-week ramp

Week	Daily volume target	Notes
Week 1	200 → 500 → 1,000 → 2,000 → 3,000	Send Mon–Fri. Skip weekends initially.
Week 2	5,000 → 7,500 → 10,000 → 15,000 → 20,000	Watch bounce and complaint rates daily.
Week 3	30,000 → 40,000 → 50,000 → 65,000 → 80,000	If rates spike, pause and investigate.
Week 4+	100,000+	Full volume — you're warm.

Always send to your most engaged contacts first — people who opened or clicked in the last 90 days. High engagement in the early days tells inbox providers your email is wanted. Save your less-engaged contacts for later in the warm-up.

Already warm on another platform? If you're migrating from Mailchimp or SendGrid and have been sending consistently, you still need to warm up in SES because your domain's IP reputation doesn't transfer. Your domain reputation does carry over partially, which means warm-up is faster — usually 1–2 weeks instead of 4.

Bounce handling

Hard bounces

A hard bounce means permanent delivery failure — the address doesn't exist, the domain doesn't exist, or the recipient's server explicitly rejected the message. SES Mailbox automatically suppresses hard-bounced addresses immediately.

Soft bounces

A soft bounce is a temporary failure — the mailbox is full, the server is temporarily unavailable. AWS SES automatically retries soft bounces for up to 72 hours. SES Mailbox tracks persistent soft bouncers (5+ consecutive soft bounces) and flags them for review.

Reviewing your bounce list

Go to Contacts → Suppression and filter by reason Bounced. You can export this list, review it, and manually remove any addresses you believe were incorrectly suppressed.

Complaint handling

A complaint occurs when a recipient clicks the spam button. SES Mailbox receives these via ISP feedback loops and immediately suppresses the address. Gmail does not provide individual complaint reports — they only report aggregate data via Gmail Postmaster Tools.

High complaint rates: root causes

Sending to contacts who don't remember opting in (old lists, purchased lists)
Sending too frequently — daily emails to a disengaged list generates complaints
Unclear or broken unsubscribe link — recipients hit the spam button as the only exit
Subject line bait-and-switch — the email content doesn't match what recipients expect

SNS bounce and complaint notifications

AWS SNS (Simple Notification Service) delivers real-time bounce and complaint events to SES Mailbox. This is how we process events immediately rather than waiting for periodic polling.

SES Mailbox sets up the required SNS configuration automatically when you connect your AWS credentials. No manual setup is needed.

Verifying SNS is configured

In the AWS SES console: Configuration → Configuration Sets. You should see a configuration set named sesmailbox with an SNS event destination for Bounce and Complaint events. If this is missing, go to SES Mailbox → Settings → AWS Credentials → Re-configure notifications.

Deliverability best practices

Authentication

All three records must be set up and passing: SPF, DKIM, DMARC
Use DMARC p=reject once fully warm — it signals a mature sender to inbox providers
Monitor DMARC reports weekly for unexpected sending sources

List hygiene

Remove contacts who haven't opened or clicked in 12+ months before warm-up
Never buy or rent email lists
Use double opt-in for new subscribers where possible — it dramatically reduces complaints
Run a re-engagement campaign before suppressing cold subscribers

Sending habits

Send consistently — sporadic large sends damage reputation more than steady volume
Send at predictable times so recipients know when to expect you
Keep campaigns focused — one clear topic per email performs better than a newsletter kitchen sink
Monitor open rates per campaign — a sudden drop often signals a deliverability issue, not just disinterest

Gmail Postmaster Tools

Set up Gmail Postmaster Tools for your sending domain. It shows your domain reputation (from Google's perspective), spam rate, and authentication pass rates. Aim for "High" domain reputation. "Medium" is acceptable. "Low" means you have a deliverability problem.