Hi,
This week I received a question: “If I increase the number of IPs I use, can I send more messages to Gmail?”
Having multiple IPs can increase the capacity of your infrastructure, but that does not mean you can multiply your sending volume by the number of IPs.
Gmail considers signals related to both the domain and the IP addresses. If you use four IPs, for example, that does not automatically mean you can send four times as many messages using the same domain.
There is also no universal number I can recommend as a safe daily volume for every sender. Capacity depends on your sending history, reputation, recipient engagement, and how your volume is distributed over time.
Domains and IPs play different roles
Think of the domain as a sending identity and the IPs as part of the infrastructure used to deliver the messages. Both need to be considered when you plan to increase your volume.
In its sender guidelines, Google explains that it tracks volume, feedback, and limits by domain and by IP. SPF and DKIM quotas are specific to the domain, while an IP’s quota is shared by the senders using it.
In practice, adding IPs does not eliminate a problem associated with the domain. Likewise, a problem with a shared IP can affect the senders who rely on it.
Before expanding your infrastructure, it is worth asking: what is limiting your operation today? The answer may lie in technical capacity, but it could also involve delivery errors, complaints, sending practices, or audience quality.
How do you define a starting volume?
Start with the volume you can already send consistently and observe the results before increasing it.
If you are introducing a new message stream, a new audience, a new ESP, or a significant infrastructure change, approach the expansion carefully.
Google recommends starting with low volumes to your most engaged recipients, avoiding spikes, and increasing sending gradually. It also recommends monitoring server responses, spam rates, and domain reputation as you grow. (If you want to accelerate this process through automation, consider using InboxAlly for warm-up.)
This does not mean everyone should follow the same daily increase percentage. Every case is different because deliverability is a distinct characteristic of each sender.
Do your recipients recognize the sender? Did they consent to receive this type of communication? Are the campaigns similar to those you already send? The answers can help you define a more appropriate starting point.
Spread out your sends and monitor the signals
In addition to daily volume, pay attention to how messages are distributed throughout the day. A campaign concentrated into a few minutes may produce a different response from one spread over several hours.
As you increase volume, monitor:
- SMTP responses: deferrals, rejections, bounces, and rate-limiting messages.
- Google Postmaster Tools: reputation, delivery errors, authentication, and spam rates.
- Campaigns: engagement, unsubscribes, and the performance of similar messages sent to comparable audiences.
- Inbox placement: where messages are detected in monitored seed mailboxes, if you use InboxAlly, for example.
These signals complement one another. A message accepted by the server did not necessarily reach the inbox, and seed results do not measure the placement of every real recipient.
For personal Gmail accounts, Postmaster Tools helps you monitor trends, but it may not display all data on low-volume days, and it can take a day or two for data to appear. Missing data should not automatically be interpreted as an absence of problems.
Google recommends keeping the spam rate reported in Postmaster Tools below 0.10% and avoiding 0.30% or higher. These numbers are only one of the factors that influence deliverability; staying within them does not guarantee that all your messages will reach the inbox.
What should you do when errors appear?
If sends begin to experience deferrals or rejections as you increase volume, stop scaling and investigate the SMTP responses. Depending on the error and how often it occurs, you may need to reduce volume while you identify the cause.
One code worth watching is 4.7.28, which Google associates with sending limits. A useful reference is smtp.codes. It lists SMTP error codes by provider and error type and points you toward solutions or actions for each case. Super useful!
It is also worth checking whether there were simultaneous changes to your audience, content, or infrastructure. When several things change at once, it becomes harder to identify what contributed to the deterioration.
What if several clients share the infrastructure?
If you send campaigns for different clients using the same infrastructure, monitor performance by client or campaign whenever possible. A problem concentrated in one message stream can be hidden in aggregate numbers.
For large-volume senders, Google Feedback Loop can identify campaigns or other groupings associated with high complaint rates. It requires a configured Feedback-ID header and compliance with the service’s requirements. (Remember that Google Postmaster Tools data relates only to gmail.com recipients.)
This breakdown helps with the investigation, but it does not replace monitoring shared reputation and delivery responses.
Capacity is built and monitored
Instead of looking for a universal ceiling or multiplying a number by the number of IPs, establish a starting volume appropriate for your history, increase it gradually, and monitor how recipients and Gmail respond.
If the signals remain healthy, you will have a stronger basis for continued growth. If errors, complaints, or a meaningful decline in performance appear, adjust the plan before moving forward.
Now tell me: how have you been doing it? Do you monitor the volume sent to Gmail both daily and hourly?
Until next time,
Fabrício
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