Hi @wwa-jvteeffelen,

do I understand correctly that this issue affects Outlook Web and New Outlook on Windows only? I suppose so because all other Outlook editions take their timezone settings from the operating system they are running on.

If yes, this issue has nothing to do with Set-OutlookSignatures itself, but with the Benefactor Circle add-on. Only the add-on writes to Outlook Web.

There may be a problem around the brand-new Graph APIs the add-on uses since 4.26.0, ExplicIT will investigate on this.
Please open a professional support request with them at https://set-outlooksignatures.com/support#professional-support - their support promise applies: If your support request is due to a bug in the latest version of Set-OutlookSignatures, the Benefactor Circle add-on, its documentation, or the provided components, support is free - no exceptions. For all other questions, you will receive the same first-class support at a fair price.

In the meantime, please test a possible workaround: Not using the new Graph APIs, but the old EWS code path (which still exists as a fallback and will work until Microsoft disables EWS in Exchange Online later this year): In your Entra ID app for Set-OutlookSignatures,

• remove the delegated Graph API permission 'MailboxConfigItem.ReadWrite'
• add the delegated Graph API permission 'EWS.AccessAsUser.All'
• grant admin consent
• Wait a few minutes (Entra can sometimes take quite some time until API permission changes are replicated)
• Run Set-OutlookSignatures and the Benefactor Circle add-on again

This forces the old EWS code path. If the issue is gone then, it is clear that there is something wrong around the new Graph APIs.