Importing large contact lists
Good news first: we fixed an issue that could stop very large contact lists (about 5,000 contacts or more) from starting to import. If you tried to import a big list and saw "Failed to start import. Please try again," the problem is resolved — just open your list and import it again, and it will start normally. Smaller lists were never affected. If you run into anything unexpected, reach out and we will help right away.
How large imports work:
When you import a contact list, WarmySender checks the file and brings your contacts in. Smaller lists finish almost instantly. Very large lists — roughly 5,000 contacts and up — are brought in for you in the background so you are never left staring at a frozen screen. After you start a big import you will see a progress bar at the top of the Contacts page, and you are free to keep working in the rest of the app while it runs. When it is done, the count updates and your new contacts are ready to use. You do not have to keep the page open or wait around for it to finish.
Preparing your file for a smooth import:
- Use a CSV file. A simple comma-separated file exported from a spreadsheet (Google Sheets, Excel, Numbers) or your CRM works best.
- Keep a header row. The first row should name your columns — for example Email, First Name, Last Name, Company — so we can map them correctly. Email is the most important column.
- Clean, plain values. Make sure email addresses are in their own column and avoid stray characters or merged cells.
- Duplicates are handled for you. If the same email appears more than once in your file, or a contact is already in your account, we recognize it and will not create a second copy — so it is safe to import a list even if it overlaps with contacts you already have.
- Very large files can take a few minutes. A list of tens of thousands of contacts is no problem; it just runs in the background and the progress bar keeps you posted.
A few things to expect:
- You can keep using WarmySender while a big import runs — set up a campaign, check your warmup, or browse other contacts. The import keeps going on its own.
- The progress bar shows how far along the import is and updates as it works through your file.
- Once the import finishes, your contacts are immediately available to add to a campaign.
Frequently asked questions:
Is there a limit to how many contacts I can import? There is no small cap — you can import very large lists, including tens of thousands of contacts at once. Large lists simply import in the background and may take a few minutes to finish.
My large import said "Failed to start import" — what do I do? This was a known issue with very large lists and it has been fixed. Please open your list and start the import again; it will begin normally. If it still does not start, contact us at [email protected] and we will sort it out quickly.
How do I know when a big import is finished? Watch the progress bar at the top of the Contacts page. When it completes, your contact count updates and the new contacts are ready to use — there is nothing else you need to click.
Can I keep using the app while it imports? Yes. Large imports run in the background, so you can keep working anywhere in WarmySender while your contacts are brought in. You can even close the page and come back later.
Will importing the same list twice create duplicate contacts? No. We automatically recognize emails that are already in your account or repeated within your file, so re-importing will not create duplicate contacts.
What file format should I use? A CSV file with a header row works best. Make sure your email addresses are in their own column. Most spreadsheet apps and CRMs can export a CSV in a couple of clicks.
Still have a question about importing? Open warmysender.com/documentation, click "Copy Prompt to Clipboard," and paste it into an AI assistant like Claude or ChatGPT along with your question — or email us at [email protected] and we will help.