Update MailService Class with Enhanced Context Handling and Warnings

[JSchmie]

Description

This pull request updates the MailService class to improve its versatility, maintainability, and compatibility with various SMTP servers.

Key Changes

• Connection Type Handling: Introduced the connection_type parameter to support different SMTP connection types ('SSL', 'TLS', 'PLAIN').

• Enhanced SSL Context Handling: Added the context parameter and refactored SSL context setup into the setup_context method, allowing for flexible SSL configurations.

• Deferred Context Initialization: Moved SSL context initialization into the setup_mailserver method for lazy initialization.

• Custom Warnings: Implemented custom warning classes for better error handling and debugging.

• Simplified Code Structure: Refactored methods and removed redundant code for improved readability.

Reason for Changes

These changes make the MailService class more flexible and robust:

• Versatile SSL Context Handling: Users can now specify SSL contexts as None, 'default', custom dictionaries, or existing SSLContext instances, accommodating various SMTP server requirements.

• Support for Multiple Connection Types: The connection_type parameter allows for easy configuration of different SMTP connection methods.

• Improved Error Handling: Custom warnings provide clearer information about errors, facilitating debugging and maintenance.

• Code Maintainability: Refactoring and code simplification enhance readability and ease future modifications.

Impact

• New Variables Introduced:

  • connection_type: Specifies the SMTP connection type ('SSL', 'TLS', 'PLAIN').
  • context_param: Stores the context parameter for later use in setup_mailserver.

• Changes to Existing Variables:

  • Removed: context_kwargs has been removed.
  • Added: context parameter replaces context_kwargs for more flexible SSL context handling.

• Modified Methods:

  • __init__: Now accepts connection_type and context parameters.
  • setup_mailserver: Calls setup_context to initialize the SSL context.
  • setup_context: New method to handle SSL context creation.
  • Removed: test_login method has been removed; its functionality is integrated into setup_mailserver.

• Backward Compatibility:

  • Breaking Changes: The interface of the class has changed due to new parameters and the removal of context_kwargs. Users will need to update their code to accommodate these changes.
  • Configuration Files: Existing configuration files will need updates to reflect the new parameters (connection_type, context) and remove deprecated ones (context_kwargs).

Testing

• Manual Verification:

  • Verified that emails are sent correctly and that attachments are handled properly.
  • Checked that warnings are issued when expected, such as on authentication failures or connection issues.
  • Ensured that the class behaves as expected when optional parameters are omitted.