Emails sent through custom SMTP provider are missing the "To" header

### 👟 Reproduction steps ## Description Emails sent using Appwrite Messaging with a custom SMTP provider appear to be delivered successfully, but the received email does not contain or display a proper `To` recipient field in email clients such as Gmail. I found another user on the Appwrite Discord with the same issue. They were also using a custom SMTP provider and were not able to find a workaround. ## Reproduction steps 1. Configure Appwrite Messaging with a custom SMTP provider. 2. Create an email message using the Appwrite Server SDK. 3. Send the email to a user or target using `Messaging.createEmail()`. 4. Open the received email in Gmail or another email client. 5. Check the visible email headers / recipient information. ### 👍 Expected behavior The delivered email should include a proper To header, and email clients should display the recipient normally. For example: From: Forumek <uset@example.com> To: Recipient Name <recipient@example.com> or at least: To: recipient@example.com <img width="375" height="64" alt="Image" src="https://github.com/user-attachments/assets/e18e48ba-dd1e-4014-b640-8dcd7c225417" /> ### 👎 Actual Behavior The email is delivered successfully, but the recipient field is missing or not displayed properly in email clients. In Gmail, only the sender is shown, and the usual To / to me / recipient information is missing from the email header preview/details. <img width="274" height="71" alt="Image" src="https://github.com/user-attachments/assets/3104abbb-9de2-4d39-a2dc-9fc78dc1b10f" /> ### 🎲 Appwrite version Different version (specify in environment) ### 💻 Operating system Linux ### 🧱 Your Environment We are using appwrite 1.9.0 selfhosted, it runs in docker compose. ### 👀 Have you spent some time to check if this issue has been raised before? - [x] I checked and didn't find similar issue ### 🏢 Have you read the Code of Conduct? - [x] I have read the [Code of Conduct](https://github.com/appwrite/.github/blob/main/CODE_OF_CONDUCT.md)