Can you check the health of IP addresses before purchasing them?

Yes, it is crucial to check the health of IP addresses before purchasing. Utilize tools from providers like Spamhaus and Talos to look up the IP's history on blacklists (or blocklists) and assess its past reputation. This can help identify any inherited issues that might affect your deliverability.

Are IP reputations permanently damaged or unrecoverable?

IP reputations are generally not permanently damaged. While an IP can accumulate a negative history, reputation can often be recovered over time through consistent sending of legitimate mail and by adhering to email best practices. Delisting from blacklists (or blocklists) is also usually possible.

Do neighboring IPs in the same Class C block affect my sending reputation?

If neighboring IPs within the same Class C block are managed by different entities and outside your specific /24 allocation, their negative actions are unlikely to significantly affect your dedicated IP reputation. ISPs typically assess reputation at a more granular level, focusing on the specific IPs under your control.

Do regional internet registries (like ARIN) delist IPs if they are not actively used?

Once an IP block is legally transferred and registered to your organization with a regional internet registry like ARIN , they are generally yours until you decide to return them. However, RIRs may require yearly justification to demonstrate active use of the assigned IP resources.

What post-purchase steps are necessary before using the IP block for mail servers?

Before using the IP block, you'll need to announce routes on them to ensure they are publicly reachable. Additionally, if the IPs were previously unused, you may need to contact bogon list maintainers to remove any flags indicating the block is unallocated. Then, you must strategically warm up the IPs by gradually increasing sending volume.

Is buying a Class C IP block a good idea for all email senders?

Buying a Class C IP block offers control but requires significant expertise and resources for ongoing management. It is often a good idea for organizations with high email volumes, specific compliance needs, or those who prefer direct control over their sending infrastructure. For lower volumes or those without dedicated email operations teams, a reputable Email Service Provider (ESP) with shared or managed dedicated IPs might be more suitable.

What are the considerations when purchasing a block of class C IP addresses for hosting mail servers? - Sender reputation - Email deliverability - Knowledge base

Many organizations consider purchasing their own block of Class C IP addresses for mail servers to gain more control over their email deliverability. This can seem like a logical step, especially for those experiencing issues with shared IP pools or seeking to scale their email operations significantly.

Class C IP addresses are defined by the first three octets determining the network address, with the last octet for hosts, typically offering 256 addresses, often referred to as a /24 block. The idea behind acquiring such a block is to isolate your sending reputation from other users, providing a dedicated infrastructure for your email campaigns.

However, this decision comes with a unique set of considerations that extend far beyond the initial purchase. From understanding the nuances of IP reputation to navigating regional internet registry policies, there are many factors to weigh.

My experience indicates that while the promise of full control is appealing, the operational realities demand careful planning and expertise.

Purchasing and evaluating IP block health

Before committing to a purchase, it's crucial to assess the historical health of the IP block you're considering. IP addresses can carry residual reputation from previous owners, which directly impacts your future deliverability. A thorough check can prevent significant headaches down the line.

You should leverage various tools to check if any of the IP addresses are currently on a public blacklist or blocklist. Services such as Spamhaus and Talos offer insights into IP reputation. Checking these proactively can help you avoid inheriting a problematic reputation, even though most IPs can be recovered.

You're not technically "buying" an IP address in the traditional sense, but rather acquiring the right to use and manage it, often through a transfer from another entity. This process typically involves regional internet registries (RIRs) like ARIN, which assign and manage IP addresses. This transfer process ensures the legal and administrative control shifts to your organization.

It's essential to perform thorough due diligence. This includes reviewing the block's history, checking for previous use in spamming activities, and ensuring clear title transfer. While brokers can facilitate this, their role is primarily transactional, so your own vetting is paramount.

Pre-purchase checks

Blacklist status: Verify current and historical listings on major blocklists (e.g., Spamhaus).
Previous usage: Investigate past email sending patterns and domain associations.
ARIN registration: Confirm the IP block's ownership and allocation details are up to date.

Why it matters

Deliverability impact: Inherited poor reputation can severely impact your inbox placement.
Warming period: A bad history may prolong the necessary IP warming period.
Recovery efforts: If an IP is blocklisted, delisting can be time-consuming.

Operational complexities and ongoing management

A common concern is whether the reputation of neighboring IPs within the same Class C block, but allocated to different entities, can affect yours. Generally, if those IPs are outside your specific /24 block and managed by different organizations, their negative behavior is unlikely to significantly impact your dedicated IP reputation. Internet Service Providers (ISPs) typically assess reputation at a more granular level than the entire Class C range. This means you have more control over your specific IP addresses.

Once an IP block is registered to your organization through ARIN, they generally cannot take it back unless you surrender it. However, regional internet registries often require yearly justification to ensure efficient use of assigned IP resources. This justification typically involves demonstrating active use of the IP addresses, which can be challenging if you're not utilizing all of them immediately for sending mail. It's important to plan your IP usage strategy carefully. Remember that "purchasing" IPs is more akin to leasing the rights to use them indefinitely, as clarified by Quora's discussion on IPv4 leasing.

Before deploying mail servers on your newly acquired IPs, you'll need to announce routes on them. This involves configuring your network to advertise that your IP block is reachable through your autonomous system (AS). Additionally, if the IP block has been unused for a significant period, it might be listed on "bogon" lists, which identify unallocated or reserved IP addresses that should not be routing on the public internet. You'll need to work with bogons list maintainers to have your newly acquired IPs removed.

Acquiring a dedicated IP block is just one piece of the puzzle. Effective email deliverability for a self-hosted mail server involves much more than simply owning IPs. You need robust infrastructure, proper DNS configuration (SPF, DKIM, DMARC), meticulous list hygiene, content optimization, and continuous monitoring to maintain a positive sender reputation and avoid blacklists (or blocklists). This is a complex undertaking that requires specialized skills and ongoing effort, as highlighted by resources like Hostwinds' guide and Colocation America's advice.

Maintaining reputation and scaling

Once you have your Class C IPs, it is critical to warm them up properly. This means gradually increasing your sending volume over time, allowing ISPs to build a positive reputation for your new IPs. Failing to warm up correctly can lead to emails being sent to spam folders or even immediate blacklisting.

Proactive monitoring is essential. You need to regularly check your IP addresses against various blacklists and blocklists, and monitor your sender reputation with major ISPs. If you find your IPs listed, swift action is required for delisting, coupled with identifying and rectifying the root cause of the listing.

As your email volume grows, you might find that a single Class C block isn't sufficient to handle your sending needs while maintaining optimal deliverability. You may need to consider acquiring additional dedicated IPs or blocks to distribute your sending load and manage reputation more effectively, especially if you send high volumes. This is where understanding how many dedicated IPs are needed becomes crucial.

The decision to purchase Class C IP addresses for mail servers is a significant infrastructure investment. It requires a long-term commitment to email best practices, security, and dedicated resources for ongoing management. While it offers unparalleled control, it also carries the full responsibility for your email program's success.

Views from the trenches

Best practices

Always check IP block history on major blacklists before purchase to avoid inherited poor reputation.

Plan your IP usage strategy carefully to ensure compliance with regional internet registry justification requirements.

Announce routes for your new IP blocks and coordinate with bogons list maintainers to ensure proper routing.

Implement a gradual IP warming process for newly acquired IPs to build a strong sender reputation with ISPs.

Invest in comprehensive DNS authentication, including SPF, DKIM, and DMARC, for all sending domains.

Common pitfalls

Failing to conduct thorough due diligence on an IP block's past usage and reputation can lead to severe deliverability problems.

Underestimating the complexity and ongoing effort required for self-hosting mail servers and managing IP reputation.

Neglecting to warm up new IPs slowly and incrementally, resulting in immediate blocks or spam folder placement.

Assuming that simply owning a Class C IP block guarantees good deliverability without proper sending practices.

Not monitoring for blocklist (or blacklist) listings, allowing reputation damage to accumulate unchecked.

Expert tips

An active market exists for IP blocks, and acquisition from RIRs like ARIN is generally straightforward.

IP reputations can almost always be recovered over time, even if they have a history of issues.

Neighboring IPs outside your /24 block, if managed by different entities, are unlikely to negatively impact your reputation significantly.

While ARIN requires annual justification for IP use, they cannot reclaim blocks once registered to you unless you return them.

Remember that securing the IP block is only the first step; effective email deliverability requires continuous operational excellence.

Expert view

Expert from Email Geeks says: Checking IPs against services like SpamHaus and Talos is crucial before purchase. Most IPs have reputation fade over time, and removal from blacklists is often possible with explanation after acquisition.

2022-10-13 - Email Geeks

Expert view

Expert from Email Geeks says: Historical reputation issues are rare and generally resolvable. The greater challenge lies in managing and optimizing the entire mail sending operation post-purchase.

2022-10-13 - Email Geeks

Final considerations

Purchasing a Class C IP address block for your mail servers can offer significant benefits in terms of control and potential deliverability. However, it's a decision that requires a comprehensive understanding of IP reputation, regional registry policies, and the complex operational demands of self-hosting email infrastructure. By conducting thorough due diligence and committing to ongoing management and best practices, you can effectively leverage dedicated IPs to enhance your email program's performance and maintain a strong sender reputation.