diff --git a/pyproject.toml b/pyproject.toml
index fe19e4f3bd..d36989c3be 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,11 +24,13 @@ typer = "^0.15.1"
 [tool.poetry.group.dev.dependencies]
 ruff = "^0.6.1"
 
+[tool.poetry.scripts]
+contact-io = "twfy_tools.utils.contact_io:app"
+
 [build-system]
 requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"
 
-
 [tool.ruff]
 extend-exclude = ["migrations", "commonlib", "scripts/historic"]
 
diff --git a/scripts/dailyupdate b/scripts/dailyupdate
index 518238a9ec..66b98ad30b 100755
--- a/scripts/dailyupdate
+++ b/scripts/dailyupdate
@@ -30,3 +30,6 @@ system './mpinfoin.pl';
 
 # update individual division votes
 system "./json2db.pl >> $cron_log";
+
+# Add yesterdays optins to mailchimp
+system "poetry run contact-io upload-yesterday >> $cron_log";
\ No newline at end of file
diff --git a/src/twfy_tools/utils/__init__.py b/src/twfy_tools/utils/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/src/twfy_tools/utils/contact_io.py b/src/twfy_tools/utils/contact_io.py
new file mode 100644
index 0000000000..953d17c727
--- /dev/null
+++ b/src/twfy_tools/utils/contact_io.py
@@ -0,0 +1,98 @@
+"""
+Interface to upload user optin information to MailChimp.
+"""
+
+from datetime import date, timedelta
+from functools import lru_cache
+
+from typer import Typer
+
+from twfy_tools.common.config import config
+from twfy_tools.common.mailchimp import (
+    InterestInternalId,
+    MailChimpHandler,
+    MemberAndInterests,
+)
+from twfy_tools.db.models import OptinValues, User
+
+app = Typer()
+
+mailing_list_name = "mySociety Newsletters"
+
+
+@lru_cache
+def get_mailing_list_internal_id():
+    client = MailChimpHandler(config.MAILCHIMP_API_KEY)
+    return client.list_name_to_unique_id(mailing_list_name)
+
+
+def get_internal_optin_id(
+    interest_group: str, interest_name: str
+) -> InterestInternalId:
+    client = MailChimpHandler(config.MAILCHIMP_API_KEY)
+
+    # get internal id for the mailing list
+    mailing_list_id = get_mailing_list_internal_id()
+    interest_group_items = client.get_interest_group(mailing_list_id, interest_group)
+    return interest_group_items.interest_name_to_id[interest_name]
+
+
+def upload_contacts(start_date: date, end_date: date):
+    """
+    Given a start and end date - get the optin_values for new users.
+    And add them to the relevant mySociety lists.
+    """
+    optin_interest_lookup = {
+        OptinValues.OPTIN_ORG: get_internal_optin_id(
+            interest_group="What are you interested in? Select all that apply",
+            interest_name="mySociety newsletter",
+        ),
+        OptinValues.OPTIN_STREAM: get_internal_optin_id(
+            interest_group="What are you interested in? Select all that apply",
+            interest_name="Democracy and Parliaments",
+        ),
+        OptinValues.OPTIN_SERVICE: get_internal_optin_id(
+            interest_group="Service interest",
+            interest_name="TheyWorkForYou",
+        ),
+    }
+
+    new_users = User.objects.filter(
+        registrationtime__gte=start_date, registrationtime__lt=end_date
+    )
+
+    members_and_values: list[MemberAndInterests] = []
+
+    for user in new_users:
+        internal_ids = [optin_interest_lookup[x] for x in user.get_optin_values()]
+        if internal_ids:
+            members_and_values.append(MemberAndInterests(user.email, internal_ids))
+
+    client = MailChimpHandler(config.MAILCHIMP_API_KEY)
+    mailing_list_id = get_mailing_list_internal_id()
+
+    client.batch_add_to_different_interest_groups(mailing_list_id, members_and_values)
+
+    print(f"Uploaded {len(members_and_values)} users to MailChimp")
+
+
+@app.command()
+def upload_mailchimp_optins(start_date: str, end_date: str):
+    """
+    Upload the optin values for new users to MailChimp.
+    """
+    upload_contacts(date.fromisoformat(start_date), date.fromisoformat(end_date))
+
+
+@app.command()
+def upload_yesterday():
+    """
+    Uploads the optin values for users who registered yesterday.
+    the end_date is a less than, so safe to say today.
+    """
+    yesterday = date.today() - timedelta(days=1)
+    upload_contacts(yesterday, date.today())
+
+
+if __name__ == "__main__":
+    app()