Sender IP
Understand the role of dedicated and shared sender IPs in warming up your inbox and maintaining strong deliverability.
Sender IP & IP Reputation
The sender IP is the internet address your emails are sent from. Its reputation strongly affects whether your emails land in the inbox or in spam.
What it is
The sender IP is the numeric address (like `203.0.113.25`) of the mail server that actually pushes your emails onto the internet.
Why it matters for deliverability
Inbox providers track how that IP behaves over time. A good IP reputation leads to better inbox placement, while a bad one can cause your messages to go to spam or be blocked.
How it works
Mailbox providers observe email volume, complaint rates, bounce rates, and engagement (opens, clicks, replies) for each IP. They assign a reputation score behind the scenes and use it when deciding whether to accept, delay, or filter your emails.
Sender IP reputation in action
Imagine you send marketing emails through an email service provider from IP `203.0.113.25`. rDNS shows `mail.example.com`, SPF and DKIM pass, and your list is clean with low complaints. Over time, Gmail and Outlook learn that mail from this IP is trustworthy and deliver more of your messages to the inbox.
Common problems
- Sending from a shared IP where other senders have poor practices, hurting your reputation.
- Suddenly sending a large volume of email from a new IP without warming it up gradually.
- High bounce rates due to old or purchased email lists.
- High complaint rates because people mark your emails as spam.
- Inconsistent sending patterns, such as long silence followed by huge sudden sends.
How to improve
- Warm up new IPs by slowly increasing daily volume instead of sending large campaigns on day one.
- Use clean, opt-in email lists and regularly remove inactive or bouncing addresses.
- Send relevant, expected content so recipients are less likely to mark it as spam.
- Monitor bounce and complaint rates via your email service provider and fix issues early.
- Coordinate sending across multiple IPs only if you truly need the volume and can maintain quality.
Best practices
- If possible, use a dedicated IP for important transactional or brand-critical emails.
- Separate transactional and bulk marketing traffic onto different IPs or subdomains when using high volume.
- Maintain a consistent sending schedule so mailbox providers can predict your traffic.
- Avoid sudden spikes in volume, especially on new or recently changed IPs.
- Combine strong IP reputation with proper authentication and list hygiene for the best deliverability.