When you use VYPER to send emails, your emails are sent through a shared IP pool, which lowers your deliverability.
To combat this, you can use your own SMTP provider.
Please go here to add your SMTP settings: https://vyper.io/user-settings/smtp
If you're an agency, you'll need to go to https://vyper.io/agency-clients/index then click "edit client details" on the client you want to edit SMTP settings for. Then scroll down to "Edit SMTP settings."