Problem Statement
The current SMTP submission authentication system in Proton Mail & Calendar requires users to authenticate with the exact email address they're sending from. This creates unnecessary complexity and limitations for power users and developers who need flexibility in email handling.

Current Limitations
Single authentication constraint: Users must authenticate with the same email address they're sending from
Token management overhead: Requires creating separate aliases and tokens for each service that needs to use different email aliases
Multi-user environment issues: Particularly problematic in systems like Ubuntu where different user accounts (root vs. logged-in user) have different usernames
Developer workflow disruption: Inconsistent with common development and email automation practices
Proposed Solution
Allow users to authenticate once with their primary Proton account credentials, then send email using any alias associated with that account.

Key Benefits
Simplified authentication: Single login enables use of all associated aliases
Reduced token management: No need to generate separate tokens for each alias
Better developer experience: Compatible with common email automation and CI/CD workflows
Enhanced flexibility: Supports multi-user environments and various use cases
Competitive parity: Matches Google Workspace functionality
Use Cases
Development environments: Using sendmail with different system accounts
Email automation: Services that need to send from specific aliases
Multi-user systems: Shared development environments with different usernames
Email management: Centralized control over multiple addresses
Technical Implementation
Allow SMTP authentication to accept the primary account credentials while permitting the MAIL FROM command to specify any alias associated with that account. This mirrors Google Workspace's approach where authentication validates the account, not the specific alias being used.

This change would significantly improve the user experience while maintaining security and aligning with industry best practices.