Some emails are not being sent when running via Orchestrator (Unattended Robot)

Help Studio
1

Hi UiPath Community,

I have an automation process that sends email notifications
to legal case handlers about their upcoming Hearing and
Pleading due dates. The process reads case data from a CSV
file, filters the relevant cases based on due date and
status, then sends HTML-formatted reminder emails to the
assigned handlers.

Here is a brief overview of how the process works:

  1. The bot reads a CSV file containing legal case records.
  2. It filters out cases where the Filed/Done column is
    marked as “Yes” or “N/A” — these are skipped.
  3. For the remaining cases, it calculates the days left
    before the due date.
  4. Based on the task type (Hearing or Pleading), it
    determines whether today is a notification day.
  5. Cases due today (DaysLeft = 0) are also included in
    the notification.
  6. The bot groups the cases per handler and sends one
    consolidated HTML email per handler using a Microsoft
    365 connection via UiPath’s Send Mail activity.
  7. There is a delay between each email send to avoid
    rapid consecutive requests.

THE PROBLEM:

When running the process through Orchestrator using an
unattended robot, only 1 out of 4 emails is being sent
successfully. The remaining emails are not being received
by the handlers. No hard error is thrown — the process
completes and only logs a Warning level message of
“Error Email” without the actual exception details.

We also noticed that some of the unsent emails appeared
in the Drafts folder of the sender’s mailbox instead of
being sent out.

IMPORTANT: When we run the same workflow directly in
UiPath Studio, all emails are sent successfully without
any issues.

What we have already checked:

  • The delay between sends is already set to 2 seconds
  • The HTML email body builds correctly (confirmed in Studio)
  • The Microsoft 365 connection is configured in Orchestrator
  • The Send Mail activity uses an Integration connection

Our questions:

  1. Could the Microsoft 365 connection in Orchestrator be
    missing the Mail.Send permission scope, causing emails
    to save as Drafts instead of sending?
  2. Is there a known issue with the UiPath Microsoft 365
    Send Mail activity saving to Drafts when run under an
    unattended robot context?
  3. Could the connection token expire mid-run when sending
    multiple emails in sequence?
  4. Would increasing the delay between sends help, or is
    this purely a connection/permission issue?

Any help or guidance would be greatly appreciated. Thank you!

2

Check below conditions:

  1. Mail.Send permission → If missing, emails may get saved as Drafts instead of sent
  2. Connection context → Ensure the Orchestrator connection is authorized for the same mailbox used in Studio
    3.Token expiry → Connection tokens can expire silently in unattended runs, causing partial sends
    4.Throttling / API limits → 2 seconds may be too low; try increasing to 5–10 seconds

Why it works in Studio uses interactive authentication, while Orchestrator uses a service connection, which may have different permissions.

3

Do you have a try catch around the send email? Anything set to ignore fails? Global error catcher thing interferring?

If it logs an error then it sounds like an error is being thrown but you are suppressing it.

4

There is a chance that you are hitting a firewall where UiPath runs the activity and then the outbound traffic is blocked by your network, so the email never sends