Moving to beehiiv with more than one subscriber export? Merge them into one list first, with a change log of every edit.

Why moving two or more lists gets messy

• The same email on two files: a reader on your Mailchimp audience who also signed up on Substack shows up in both exports, often with different fields filled in.
• Small differences hide repeats: the same address typed with capitals, or with a stray space at the start or end.
• Upload order matters: beehiiv updates subscribers already on your list, and by default a blank cell in the later file deletes the current value (beehiiv’s words are below).
• After an upload you see counts, not rows: beehiiv’s import history shows an uploaded, accepted and rejected count.

This page is for several exports you merge first; if you have just one file to clean before upload, see beehiiv subscriber CSV cleanup.

What beehiiv’s help page says

beehiiv’s help article on CSV uploads says “If you import emails that are already on your list, beehiiv updates those existing subscribers instead of adding new ones.” About the Overwrite existing custom field data toggle: “On (default): Values in your file replace existing values. A blank cell deletes that subscriber's current value.” And about the import history: “The system does not provide a list of specific rejected email addresses or individual rejection reasons per email.” (beehiiv Help: common concerns with CSV uploads, read 31 October 2026).

So uploading exports one after another can wipe a value you had. Merging first means one upload, with each value kept on one row and every merge listed in a change log you can read before you upload.

Two beehiiv file rules to know

The same article lists these, word for word:

• “Your CSV must have one of these headers in the first column: "email", "email address", or "emailaddress" (case-insensitive).”
• “Every row must have a valid email address in the first column.”

Our cleaned file starts with the name column, and it keeps rows with a missing or invalid email so that nothing is deleted without you seeing it. That is why steps 4 and 5 below are yours to do before you upload.

What we don’t do

• We don’t move posts, subscribe forms, automations or settings. We only work on the subscriber CSV you send us.
• Nothing inside beehiiv, Mailchimp, Substack or Kit: we don’t log in to any of them.
• We don’t predict or explain beehiiv’s rejections. beehiiv runs its own checks when you upload, and we can’t see them from your file.
• We don’t check whether a mailbox exists or will accept mail.
• Columns are not matched to your beehiiv custom fields. Your columns come back with the same headers, and you match them when you upload.
• Who you may email is your call. A cleaned file is not permission to email anyone.

Before you upload to beehiiv

1. Move the email column to first.
2. Delete the rows marked for review (missing or invalid email). They’re the rows with needs_review in the status column.

What you get back

• One row per email: same-email duplicates merged, ignoring capitals and spaces at the start or end; every merge is listed in the change log with its row numbers
• Where one row has a value and the other row with that email has the cell blank, the merged row keeps the value, and the fill is listed in the change log
• Where merged rows both have a value and they differ, the first row’s value is kept and the other value is listed in the change log
• If a status column disagrees between merged rows (for example active on one, unsubscribed on the other), the kept row is marked for review with both values in qa_notes
• Possible duplicates noted, never merged: rows with the same full name and company but a different email get a “possible duplicate” note in qa_notes and are marked for review
• Rows with a missing or invalid email kept and marked for review, so you decide what to delete

Free CSV Preflight Start a Quick Clean · $25