When you migrate from one Email Service Provider (ESP) to another, you may notice a temporary drop in deliverability metrics after your first send. This is expected and manageable with the right preparation.
This article explains why metrics change during an ESP switch and what to do to protect your sender reputation during the transition.
Before You Begin
Before sending your first email campaign on Omnisend after migrating:
Verify your sender domain. Set up SPF, DKIM, and DMARC records in your DNS settings. Without authentication, your emails are more likely to land in spam. Learn how to set up your email sender domain in Omnisend.
Confirm your sending domain or subdomain has MX records. Some mailbox providers, including Apple Mail and Comcast, reject emails sent from domains that are not configured to receive email. Check that your sending domain has valid MX records before your first send.
Set up branded click tracking links. Using your own domain for click tracking reduces the risk of tracking URLs being flagged by spam filters and builds trust with inbox providers. Learn how to set up a custom tracking domain.
Clean your imported contact list. Remove Contacts who have not opened or clicked an email in the past 6–12 months, as well as any hard-bounced or invalid addresses from your previous ESP.
Do not send to your full list immediately. Start with your most engaged Contacts and increase volume gradually over 2–4 weeks.
Why Deliverability Metrics Change After an ESP Switch
Your deliverability metrics can be affected for several reasons:
1. Your message content changed. Any significant change to your emails can affect how inbox providers evaluate them:
New email layout or template
New sender name or From address
Each ESP also sends from its own server infrastructure. Anti-spam filters detect this infrastructure change and may apply increased scrutiny to your emails until your sending pattern is established on the new platform.
2. Your domain authentication changed or was not carried over. Switching ESPs often means reconfiguring SPF, DKIM, and DMARC records. If these records are missing in Omnisend, inbox providers may filter your emails even if they reached the inbox with your previous platform. Set up your sender domain in Omnisend.
3. Inbox providers (ISPs) need time to re-evaluate your sending patterns. Major inbox providers like Gmail, Yahoo, and Outlook maintain their own records of how recipients interact with your emails. When you start sending from a new platform, they treat you as a new sender, even if your domain is the same. This adjustment period typically lasts 2–4 weeks with consistent, gradual sending. Focus on engagement trends over time rather than individual campaign results.
Warming Up Your Sender Reputation
Domain warm-up is required when you switch ESPs. This applies even if you previously warmed up your domain on another platform.
Why is a warm-up always required after switching? Inbox providers associate sender trust with both your domain and the sending infrastructure (the IP addresses and servers used to deliver your emails). When you switch platforms, your emails come from Omnisend's servers rather than your previous provider's. Inbox providers have no history of your domain on this infrastructure and treat you as a new sender, regardless of your prior sending history.
How to warm up effectively:
Start with your most engaged Contacts – those who opened or clicked an email in the past 30–90 days.
Keep daily volume growth between 25–35% per send.
Avoid sudden jumps in list size or send frequency.
Monitor open rates, bounce rates, and spam complaints after each send.
For a step-by-step warm-up plan, see How to Warm Up Your Domain Manually in Omnisend.
Contacts who have been inactive for more than 6–12 months are a common cause of hard bounces, spam complaints, and spam trap hits. Sending to unvetted imported lists can trigger Omnisend's automatic sending suspension if your bounce rate exceeds 7%.
FAQ
Do I need to warm up my domain if I'm keeping the same domain I used on my previous ESP?
Yes. Even if your domain has a strong history on another platform, you still need to warm it up on Omnisend. Mailbox providers associate sender trust with both your domain and the sending infrastructure. When your emails come from Omnisend's servers instead of your previous provider's, inbox providers treat you as a new sender. Allow 2–4 weeks of gradual sending before expecting metrics to match your previous platform.
How long will my open rates be lower after migrating?
Deliverability typically stabilizes within 2–4 weeks with consistent, gradual sending. A short-term drop is not a sign of failure – it is a normal transition. Avoid comparing raw open rates between platforms during the first month and focus instead on positive engagement trends.
My test email landed in spam. Does that mean my campaigns will too?
Not necessarily. If you sent the test email to an address on the same domain as your sender address (for example, sending from [email protected] to [email protected]), many inbox providers will filter it automatically – this does not reflect how real recipients will experience your emails.
Always test deliverability using a personal Gmail or Outlook address on a different domain, and check all folders, including Spam, Promotions, and Social.
What if my metrics don't recover after 4 weeks?
If your deliverability does not improve after 4 weeks of consistent, gradual sending to engaged contacts, contact our Support Team via in-app chat or at [email protected].
Our award-winning Support Team is available to assist you through the in-app chat or by email at [email protected].