Hi PD, this error is not related to the number of recipients in your email itself. Even when sending to a single recipient, the message “Policy-SCO1 You've reached your sending Limit” comes from your mail server, not from Mozilla Thunderbird. It usually means that your account has hit a temporary sending limit imposed by the email provider, for example due to too many messages sent in a short period, background or stuck messages being sent from the outbox, or security/rate-limiting protections triggered by the server. Sometimes hidden CC/BCC fields, mailing lists, or synced devices can also cause extra outgoing messages without it being obvious. To troubleshoot, check your Outbox and Sent folders for stuck or repeated emails, make sure no automatic CC/BCC rules or templates are adding recipients, and if possible try sending the same email via webmail to see if the issue also occurs there. If it does, the limitation is definitely server-side and not caused by Thunderbird. In that case, the best solution is usually to wait for the temporary limit to reset and contact your email provider to ask specifically about the “Policy-SCO1 sending limit” on your account.