Why are Gmail emails deferred or undelivered only to Italian subscribers after switching ESPs and subdomains?
Michael Ko
Co-founder & CEO, Suped
Published 18 Jun 2025
Updated 17 Aug 2025
7 min read
Dealing with deferred or undelivered emails, especially when it's limited to a specific demographic like Italian subscribers after switching email service providers (ESPs) and subdomains, can be incredibly puzzling and frustrating. You've done the right things: chosen a new subdomain, moved to a new ESP, and focused on highly engaged recipients. You've even checked that your domain isn't on any major blocklist (or blacklist) and your IPs show excellent SenderScore.
My immediate thought often goes to the warmup period, which is crucial for any new sending infrastructure. Two days, as you mentioned, is very short in the world of email deliverability. Gmail and other major mailbox providers need time to build trust with your new sending domain and IP addresses. This initial phase is often characterized by fluctuations in delivery, including deferrals, as the systems assess your sending patterns.
The fact that this issue is unique to Italian subscribers, while other countries are performing well, adds a unique layer of complexity. It suggests something more nuanced than a general warmup problem, although warmup definitely exacerbates any underlying issues. We need to look at both the standard challenges of migration and the specifics of targeting a particular geographical audience.
The immediate impact of ESP and subdomain changes
Migrating to a new ESP and setting up a new subdomain, even one like news.domain.com, is essentially like starting fresh with your sender reputation. Even if your corporate domain has a stellar history, the new subdomain needs to earn its stripes. Mailbox providers, including Gmail, view new sending identities with caution until a positive track record is established. This is a normal part of the process, but it can be frustrating if you're not prepared for potential dips.
A common deliverability issue during new IP and subdomain warmup is encountering deferrals. Gmail, for instance, often defers messages rather than rejecting them outright if it detects unusual sending patterns from a new or unfamiliar sender. This behavior is a protective measure against potential spam. As SpamResource explains, deferred messages remain in your sending server's queue, waiting for a retry, which accounts for the delays. You can read more about Gmail's new spam-related rejections and deferrals.
While your SenderScore of 99 is excellent, indicating your IP isn't on major blocklists (or blacklists), it doesn't immediately translate to perfect inbox placement with a new sending identity. Mailbox providers consider many factors, including domain reputation, which takes time to build on a new subdomain. It's a phased process that requires careful management of sending volume and recipient engagement.
Ultimately, switching ESPs impacts your deliverability regardless of how good your previous setup was. Every transition comes with a period of adjustment. The goal is to minimize this disruption by following a structured warmup plan and closely monitoring your metrics.
Geographic and audience-specific challenges
The most puzzling aspect of your situation is the exclusive impact on Italian subscribers. This geographic specificity points towards a few potential areas of investigation. First, consider the source and quality of your Italian subscriber list. While you're targeting highly engaged recipients, it's worth asking if this specific segment has any unique characteristics. For example, was this list acquired differently or is it significantly older than your other segments? Issues like a higher concentration of inactive addresses or even spam traps could be at play.
Another factor could be the previous ESP's handling of these addresses. If your old provider was suppressing a significant number of problematic Italian addresses (e.g., those bouncing, marking as spam, or being inactive) and this suppression list wasn't fully migrated or applied to your new infrastructure, you might suddenly be sending to a much less engaged or even harmful segment. This could lead Gmail to suddenly reject or defer more emails.
While less common for a global provider like Gmail, there could also be subtle nuances in how certain countries or regions are perceived regarding email traffic. Sometimes, localized spam trends or specific network routing issues can influence deliverability to a particular geographic area, even if your general reputation is good elsewhere. This is harder to pinpoint without more specific data from the mailbox provider.
Diving into technical and data analysis
To truly diagnose what's happening, the most crucial pieces of information are the bounce and deferral messages (also known as Non-Delivery Reports or NDRs). While you mentioned there are no bounces, the deferrals should generate specific error codes. These messages provide precise reasons from the receiving server for why an email was not immediately accepted. Your ESP should be able to provide these, or you might find them in your server logs. Without them, it's like trying to solve a puzzle blindfolded.
You also need to set up and diligently monitor Google Postmaster Tools (GPT). It can take a few days or even weeks for data to appear, especially for new sending domains, but this is the authoritative source for Gmail's perception of your sender reputation, spam rates, and delivery errors. The Gmail email sender guidelines are critical to follow for optimal delivery.
Before ESP Migration
Established Reputation: Corporate domain with long sending history, trusted by mailbox providers.
Mature Warmup: IP and domain fully warmed up, allowing high volumes.
Consistent Metrics: Predictable inbox placement and open rates across all geographies.
Suppression Lists: Previous ESP likely maintained active suppression lists for problematic addresses.
It's also worth double-checking your email authentication. Ensure that your SPF, DKIM, and DMARC records are correctly set up for the new subdomain and align properly. Even a small misconfiguration can cause delivery issues, particularly with stricter mailbox providers. For example, here's a basic DMARC record:
Finally, given the regional specificity, consider the content itself. Are there specific elements in the Italian-targeted emails that differ from your other campaigns? This could include different language modules, character encodings, or even specific links or images that might be triggering filters in Italy or for Google's systems when dealing with that specific locale. It's a long shot, but worth ruling out.
Views from the trenches
Best practices
Start your warmup with very small volumes to your most engaged subscribers.
Continuously monitor your domain and IP reputation using tools like Google Postmaster Tools.
Ensure all DNS records (SPF, DKIM, DMARC) are correctly configured and aligned for your new subdomain.
Maintain strict list hygiene, especially after migrating from a different ESP, by regularly cleaning inactive addresses.
Common pitfalls
Rushing the warmup process by sending too much too soon, leading to reputation damage and deferrals.
Failing to obtain or analyze detailed bounce and deferral messages (NDRs).
Not thoroughly migrating or accounting for previous ESP's suppression lists.
Troubleshooting too early in the warmup period when delivery patterns are still erratic and unreliable.
Expert tips
Be patient during warmup; initial delivery can seem random and volatile, but it often stabilizes over time.
Focus on segmenting your audience based on engagement, especially when introducing new sending infrastructure.
If a regional issue persists, investigate technical nuances like content encoding or language modules.
Utilize an
Expert view
Expert from Email Geeks says: Two days is a very short period for warmup, and erratic delivery behavior is expected in the initial phase. Deliverability is about probability and statistics, so you need more data.
2023-12-01 - Email Geeks
Expert view
Expert from Email Geeks says: It is tough to diagnose issues with a small sample size; deliverability relies on larger statistical patterns for meaningful analysis.
2023-12-01 - Email Geeks
Navigating deliverability after migration
Navigating the complexities of email deliverability after an ESP and subdomain migration requires a multi-faceted approach. The initial deferrals and undelivered emails, especially to a specific segment like Italian subscribers, are likely a combination of the new infrastructure's warmup phase and potentially some underlying list or content-related issues specific to that audience.
My advice would be to continue with your warmup plan, gradually increasing volume while closely observing Google Postmaster Tools for reputation changes. Simultaneously, try to obtain those critical bounce and deferral messages from your ESP. Understanding these specific errors will provide the most direct path to identifying and resolving the problem.
Remember that deliverability is a marathon, not a sprint. Patience, combined with diligent monitoring and a systematic approach to troubleshooting, will be key to getting your emails consistently to the inbox for all your subscribers, including your Italian audience. Don't forget to leverage tools for ongoing blocklist monitoring and DMARC monitoring to stay on top of your sender health.
Gmail, view new sending identities with caution until a positive track record is established. This is a normal part of the process, but it can be frustrating if you're not prepared for potential dips.
Google's systems when dealing with that specific locale. It's a long shot, but worth ruling out.
