Wrong sender name when using Gmail API

Hello,

I’m having an issue with the sender name when sending emails through Post SMTP using the Gmail API.
All emails are being delivered successfully, but Gmail always shows the sender as “Lysiane” instead of my desired name “My Travel Planner”.

Here’s the full context and what I’ve already checked: ✅ Current setup

• Website: https://www.mytravelplanner.io
• Mailer type: Gmail API
• Post SMTP is configured correctly (emails send successfully)
• Sender Name in Post SMTP → Message tab: My Travel Planner
• “Prevent plugins and themes from changing this” is checked
• Directorist plugin (which triggers automated emails) also set to “My Travel Planner” as sender
• Gmail account used: [email protected]

🔍 What happens

• All outgoing emails arrive correctly.
• But the sender name always appears as “Lysiane” (the personal name of the Gmail account owner) instead of “My Travel Planner.”
• Previously, when I was using my host’s SMTP server (helicoptere.o2switch.net), the sender name appeared correctly as My Travel Planner.
• This issue only started after switching to Gmail API authentication.

🧩 What I’ve tried

1. Confirmed “From Name” = My Travel Planner in all plugins (WordPress General Settings, Post SMTP, and Directorist).
2. Checked Gmail settings → “Send mail as” already set to My Travel Planner.
3. Deleted OAuth access and reconnected Gmail API.
4. Reinstalled Post SMTP.

Emails are still sent fine, but Gmail keeps replacing the display name with “Lysiane.” ❓ What I need help with

Is there any way to force Post SMTP / Gmail API to use the custom “From Name” instead of the Gmail account’s personal name?
Or can this be overridden through Post SMTP configuration or a filter?

Thanks a lot for your help!
— Lysiane
(https://www.mytravelplanner.io)