5.7.57 SMTP in scheduled task

Question

5.7.57 SMTP in scheduled task

Aleksej Egorov 41

Hello everyone. I’m trying to send an email from a scheduled task but am encountering an error. However, the script runs perfectly fine in an interactive session. I see the same behavior whether I use Send-MailMessage or the Send method of System.Net.Mail.SmtpClient.

Everything works fine if I provide the sender's credentials explicitly (either hardcoded or by importing them via Import-CliXml). In the previous installation on Server 2022 everything also was fine.

Client OS Version: 10.0.26100
PSVersion: 5.1.26100.33438
Exchange OS version: 10.0.26100
Exchange Server version: 15.2 (Build 1748.10)

Any ideas?

0 comments

Answer accepted by question author

Deepesh Dhake 1,245

The most likely cause is Credential Guard, which Server 2025 enables by default on domain-joined servers. Your 2022 box probably didn’t have it.Check:

(Get-CimInstance -Namespace root\Microsoft\Windows\DeviceGuard -ClassName Win32_DeviceGuard).SecurityServicesRunning

If the output includes 1, it’s on. Test with it disabled.

Also rule out: the task set to "Do not store password" (no network credentials), or running as SYSTEM (authenticates as COMPUTER$).

Fix: keep using Import-CliXml (create the file as the task’s account on that server), or use an IP-scoped relay connector.

Aleksej Egorov 41 Reputation points

2026-10-14T09:55:21.8966667+00:00

Yep, you're right, it was Credential Guard! Thanks a lot!

1 additional answer

Your answer

Aleksej Egorov 41 Reputation points

2026-10-14T09:55:21.8966667+00:00

Yep, you're right, it was Credential Guard! Thanks a lot!

Answer 1

Hello @Aleksej Egorov

Welcome to Microsoft Q&A!

Thank you for your patience, and taking the time to elaborate on your concerns.

This difference is expected: scheduled tasks run under a non‑interactive logon type and do not inherit cached credentials from your interactive session. That’s why implicit authentication fails, but explicit credentials succeed.

Key Points.

Interactive vs. scheduled context: Interactive sessions can reuse cached Kerberos/NTLM tokens; scheduled tasks cannot.

Task Scheduler logon type: Runs as LOGON_BATCH, which restricts credential delegation.

OS changes: Newer Windows builds enforce stricter credential handling compared to Server 2022.

Fix Options.

Run the task under a service account with SMTP permissions.

Store credentials securely using Export-CliXml / Import-CliXml and load them in the script.

Check Task Scheduler settings:

“Run whether user is logged on or not” (requires stored password).

  “Run with highest privileges.”
  
  Consider modern authentication (OAuth, certificates) if your Exchange/SMTP server supports it.

Relevant Documentation.

PowerShell Send-MailMessage cmdlet (learn.microsoft.com in Bing)
Scheduled Tasks and Security Context (learn.microsoft.com in Bing)
About PowerShell Credentials (learn.microsoft.com in Bing)

Note: Scheduled tasks don’t inherit your interactive credentials. Use a service account or securely stored credentials (Import-CliXml) to ensure reliable email sending. Modern auth methods are recommended if available.

I hope this helps to better understand the diagnostic options available and the risks involved.

If this information was helpful, please click Accept Answer.

Thank you for choosing Microsoft Q&A.

Ronald Sabiiti 585 Reputation points Independent Advisor

2026-10-14T08:06:54.2633333+00:00

Hello @Aleksej Egorov

I hope you’re doing well. I’m following up to check whether the suggested solution resolved your issue.

If this information was helpful, please click Accept Answer. Doing so helps other community members identify useful solutions to similar issues.

Thank you for choosing Microsoft Q&A!