Why warming up a subdomain can be challenging?
The warm-up process is a time when senders are gradually increasing email volume, but inbox providers haven't fully approved them yet. This can affect email delivery.
Why? Inbox providers use automated security checks to limit emails from new senders or those with inconsistent sending habits. These checks protect users from spam.
What kind of checks? Inbox providers have many tools to identify untrustworthy senders. One of them is the reputation itself, but they also use advanced spam filters, block lists, and more.
While complete blocking is a possibility, email providers typically employ a range of actions to manage sender reputation and filter emails, impacting deliverability.
How to behave in case of delivery issue?
Focus on building trust and improving deliverability
Email providers track your sending activity over time. This includes factors like IP addresses, sending domains, and even the unique fingerprint of your email templates.
There is no instant fix.
A practice known as "snowshoe spamming" involves spreading email blasts across numerous IPs and domains to bypass spam filters.
Spammers often resort to tactics like sending mass emails from a single domain and IP, then rapidly switching to new ones once blocked. Doing the same thing to evade timeouts in case of delays or a block can confirm you are a spammer.
In short, while it might seem like a clever tactic, it can backfire and damage your sender reputation in the long run. :
Negative impact on reputation: Email providers can easily identify snowshoe spamming attempts, which can significantly harm your sender reputation. This could lead to future emails being filtered as spam or even blocked entirely.
Reduced deliverability rates: A tarnished sender reputation translates to lower email deliverability rates. This means fewer of your emails will reach their intended recipients' inboxes.
Patience is key
While email is a powerful communication channel, resolving delivery issues can be stressful, especially when lots of essential emails for your business are rejected.
Mitigation processes take time.
In average, block lifts to take at least a week, depending on the inbox provider.
This delay reflects the complex nature of the mitigation process:
Response time: Response times for support tickets submitted to inbox providers can range from 24 to 48 hours. Unfortunately, some providers may take even longer.
Weekend delays: Most deliverability teams at inbox providers don't operate over weekends. This adds another layer of delay to potential mitigation efforts. This is an important point, because some providers are known for blocking IPs late on Friday.
Additional information requests: Even after submitting a ticket, the inbox provider's team might request further details about your company, sending practices, and more information before lifting a block.
Resume slowly: Don't jump back to your previous sending volume immediately. Start cautiously and gradually increase your sending rate to avoid potential re-blockages.
Low open rates
Symptoms & detection
Low open rates, only for a specific inbox provider.
This can be detected by comparing the open rate for the same campaign or same sender, across several inbox provider (e.g. two times lower, or more).
Explanation & mitigation
Emails coming from your newly created subdomain are accepted by the inbox providers. Due to your neutral reputation, you are not trusted as a sender.
This is a known behavior for Microsoft (e.g, Hotmail / Live / Outlook).
Most inbox providers will accept your emails, but:
They will place most of them into the spam folder.
The rest will serve as a "control group" to see if users expected your email and engage with it (e.g. open, click, forward, answer, archive) or if they ignore it (e.g. delete without reading) or show signs of irritation (e.g., unsubscribe, spam complaint, etc). Based on that, more emails will be placed in the main inbox.
Short term mitigation plan
While your new subdomain establishes its reputation, maintain your sending schedule as planned.
However, prioritize targeting highly engaged users with contextually relevant content. This approach increases the likelihood of positive user interactions, which signal legitimacy to inbox providers.
Medium term mitigation plan
Review your email activity: Check your email and sender scoring for Microsoft (see more here). This can help identify campaigns or automations negatively impacting your reputation.
Check other performance indicators: Bounce rates, unsubscribe rates, spam complaint rate.
Check Microsoft SNDS: If you are using a dedicated IP, use SNDS (see more here) to see the most recent spam complaints. Try to understand the profile of subscribers who filed spam complaints and for which email.
Long term mitigation plan
If you don't find any reason explaining the issue, please contact your Customer Success Manager. Batch's Delivery Manager will investigate the issue and may open a ticket with the inbox provider's deliverability team.
Delivery delays
Symptoms & detection
Delays happen when inbox providers temporarily refuse emails (from several minutes to several hours).
Batch will retry gradually every minute, then at increasing intervals over hours. If, after 24 hours, the email hasn't been delivered, Batch will cancel the delivery of the delayed emails. These will be classified as "soft bounces", in the category "transient failure".
📌 Concerned inbox providers: Microsoft, AOL, Comcast and 1&1 (e.g. web.de/GMX).
Explanation & mitigation
Delays and rate-limiting can happen for several reasons.
First stages of the warm-up
In the context of a new subdomain warm-up, these delays are especially common during the first week when mailbox providers haven't yet established trust with the domain.
German mailbox providers such as 1&1 (e.g. web.de/GMX) will initially delay most of the emails coming from new senders to analyze their authentication, see how users interact with the emails that went through, then lift the rate limit. This usually lasts 48h to 72h and cannot always be mitigated by opening a ticket.
Short-term mitigation plan
Keep sending emails, following your migration schedule.
Make sure you target engaged users in a contextual manner to increase your chance of being considered as a legitimate sender thanks to the positive feedback they provide.
Medium term mitigation plan
If you don't find any clear reason why the delays are not lifted, please contact your Customer Success Manager. Batch's Delivery Manager will investigate the issue and may open a ticket with the inbox provider.
Reputation issue
Even after the one week of warm-up without issues, inbox providers can start delaying the delivery of your emails.
This can happen when they have a doubt on your trustworthiness as a sender due to:
Poor engagement performances and high bounce rates.
Bad sending permanence (e.g. you stopped your warmup for 4 days and resumed it suddenly).
A hurried migration schedule.
This should be considered as a red flag you need to address shortly, a warning sign that often precedes a block on your subdomain or sending IP address.
Short-term mitigation plan
Analyze your email activity considering the day when you started noticing delays:
Engagement issue: Did you notice an abnormal unsubscribe/spam complaint pike?
Identify the campaigns or automations and pause them, while you are working on improvements.
Review the targeted audience of these campaigns and see if it should be adjusted.
Sending permanence issue: Did the issue occur after a "pause" in your migration schedule?
Avoid any pauses during a warm-up process. When resuming your warm-up after a pause, don't go straight away to the next stage increasing the sent emails volumes. Start again, on the previous step.
Make sure volumes increase gradually, they shouldn't decrease. Inbox providers need to be able to understand your sending patterns.
Sending volumes issue: Did the delays started after a substantial increase of the sent email volumes?
Adjust your migration schedule to increase in a slower way the volume of sent emails in every stage.
Create a separate campaign targeting exclusively that inbox provider, resuming the warm-up in a slower way until the delays disappear.
Medium term mitigation plan
If after several days you are still noticing delays and emails are not accepted after 24h, causing lots of soft bounces, alert your Customer Success Manager. Batch's Delivery Manager will investigate the issue and may open a ticket with the inbox provider.
Blocks
Symptoms & detection
If inbox providers consider your email activity represents a threat, they can refuse emails sent from:
A specific subdomain
All the subdomains tied to your main domain
The sending IPs you are using (dedicated or shared IPs)
The level at which the block is applied depends on each inbox provider. For example, Google tends to block subdomains, while Microsoft tends to apply restrictions at the IP level.
The symptoms are a high amount of block bounces, for most or all of your emails:
Explanation & mitigation
Automatic IP blocking
New dedicated IPs, which have no sending history with inbox providers, are more likely to be blocked by spam filters. This is usually the case with dedicated IPs, as opposed to shared IPs that have already been warmed up for you.
Some of the inbox providers applying these rules are:
🌎 Microsoft (Office 365): Your new IPs might be blocked by default. Microsoft's professional email services will send a bounce message stating "
Access denied, banned sending IP [w.x.y.z]. To request removal from this list please visit https://sender.office.com/ and follow the directions." You can manually request mitigation here: https://sender.office.com/ (know more here). This doesn't appear to impact Microsoft's consumer mailboxes (e.g. hotmail.com, live.com, outlook.com). Sending IPs are unblocked in 48h after the unlist request.
🇩🇪 T-Online: T-Online usually blocks new IPs unless a mitigation request is sent to their support team. Please note that a mitigation cannot be requested before you send your first emails, as T-Online needs to analyze the blocked email traffic to see if you are a legitimate sender. The mitigation must be requested by Batch's delivery manager and can take between 2 to 4 days.
🇩🇪 United Internet (GMX, Web.de, etc.): United Internet may block your email for a few days before lifting the block automatically once it has been properly analyzed.
Other block bounces issues
Inbox providers can decide to block your IP(s) or domain(s) after accepting your emails for the first few days. The information motivating that decision can come from:
Internal Data: Sending history, engagement history, etc. When this happens, the block will occur for this provider only. If it's motivated by bad practices, other blocks should follow shortly after from other inbox providers.
External Data: Independent block lists (see more here). The block issue should appear for several inbox providers, as some blocklists are used widely.
🌎 Microsoft Consumer Mailboxes (OLC): If you are noticing constant delivery delays, consider this a warning. You should review your email activity. Transient failure issues (meaning, email delivery expiring after 24 hours of retry) are a warning sign of an imminent block.
In rare occasions, blocks can be lifted automatically after a few days. Before opening a ticket, the possible causes must be identified to prove to inbox providers that you have done everything needed (e.g., retiring the automation causing the issue, fixing the targeting issue, etc).