How IP Reputation Works
Every IP address that sends email has a reputation score maintained by mailbox providers. This reputation is built over time based on the sending behavior observed from that IP:- Bounce rates — How often emails from this IP are sent to invalid addresses
- Complaint rates — How often recipients mark emails from this IP as spam
- Volume consistency — Whether sending patterns are predictable or erratic
- Spam trap hits — Whether emails from this IP are sent to known spam trap addresses
- Engagement signals — Whether recipients open, click, and interact with emails from this IP
Shared IPs
With shared IPs, your emails are sent from IP addresses that are also used by other senders on the same ESP. Your reputation is pooled with theirs.How Shared IPs Work
The ESP manages a pool of IP addresses and distributes sending across them. Multiple customers send email from the same IPs. The reputation of those IPs reflects the aggregate behavior of all senders using them.Advantages
Disadvantages
Reputable ESPs mitigate shared IP risk by enforcing strict sending policies, monitoring for abuse, and quickly removing bad actors from shared pools. The shared IP risk is real but manageable with a well-run ESP.
Dedicated IPs
With a dedicated IP, your emails are sent from an IP address used exclusively by your account. Your reputation is entirely your own — built by your sending behavior alone.How Dedicated IPs Work
The ESP assigns one or more IP addresses to your account. All email from your account is sent from those IPs and no one else’s email uses them. Your reputation on those IPs is determined solely by your sending practices.Advantages
Disadvantages
When to Use Each Option
Use Shared IPs When
- You send fewer than 50,000 emails per month
- Your sending volume fluctuates significantly (seasonal business, event-driven spikes)
- You are starting out and do not have the volume to sustain a dedicated IP
- You want to start sending immediately without a warm-up period
- You are a small to mid-size sender who wants the ESP to manage IP reputation
Use Dedicated IPs When
- You consistently send more than 100,000 emails per month
- You need full control over your sender reputation
- You operate in a regulated industry where reputation isolation is required
- You have the resources to manage IP warm-up and monitor reputation metrics
- Your deliverability requirements are strict (financial services, healthcare notifications)
The Gray Zone: 50,000–100,000 Emails Per Month
Senders in this range can go either way. Consider a dedicated IP if:- Your content or audience puts you at higher risk for complaints (e-commerce promotions, user-generated content notifications)
- You have experienced deliverability issues on shared IPs that you suspect are caused by other senders
- You want the ability to directly correlate your sending practices with your deliverability outcomes
IP Warm-Up
If you move to a dedicated IP, you must warm it up before sending at full volume. A new IP has no reputation — mailbox providers do not know whether to trust it. Sending thousands of emails from an unknown IP will trigger spam filtering.Warm-Up Schedule
A typical warm-up schedule gradually increases daily volume over 4–6 weeks:Warm-Up Rules
Start with your most engaged recipients
Start with your most engaged recipients
During warm-up, send to recipients who have recently opened or clicked your emails. Their positive engagement sends strong trust signals to mailbox providers. Save less-engaged segments for later in the warm-up process.
Send every day without gaps
Send every day without gaps
Consistency matters during warm-up. Send every single day, even weekends. Gaps in sending can reset the reputation-building process or make the IP look inactive. If you do not have enough daily volume to fill the schedule naturally, consider supplementing with engaged segments from your list.
Monitor bounce and complaint rates at each stage
Monitor bounce and complaint rates at each stage
Watch your bounce rate (should stay below 2%) and complaint rate (should stay below 0.1%) at every volume step. If either metric spikes, pause volume increases and investigate before continuing. Pushing through bad metrics will damage the IP’s reputation.
Do not skip steps
Do not skip steps
It is tempting to accelerate warm-up to reach full volume faster. Resist this. Mailbox providers need time to observe consistent, positive behavior. Jumping from 500 to 50,000 emails per day will trigger throttling and filtering that can take weeks to recover from.
Separate warm-up by mailbox provider
Separate warm-up by mailbox provider
Gmail, Outlook, and Yahoo each maintain independent reputation data. Your IP may warm up faster with one provider than another. If you see filtering from a specific provider, reduce volume to that provider’s domains while continuing normal volume to others.
Domain Reputation vs IP Reputation
IP reputation was historically the dominant factor in filtering decisions, but the industry has shifted significantly toward domain reputation. Major mailbox providers — especially Gmail — now weight domain reputation more heavily than IP reputation.Multiple Dedicated IPs
High-volume senders sometimes use multiple dedicated IPs to separate different email streams:
This approach provides maximum reputation isolation but adds operational complexity. Each IP needs its own warm-up, monitoring, and volume management. Only pursue this if your volume and deliverability requirements justify the overhead.
Related Topics
What Is Email Deliverability?
How IP and domain reputation fit into the broader deliverability picture.
Sending Reputation
Build and protect your sender reputation across IPs and domains.
Deliverability Best Practices
Practical strategies for maximizing inbox placement including warm-up guidance.
Subdomain vs Root Domain
Domain strategy for isolating email streams and protecting reputation.