Expand POP3 client documentation with numerous Aspose.Email usage samples

[agent-aspose-email-examples]

Automated submission from agentic runner.

Change summaries (LLM):
Added example demonstrating POP3 mailbox message count retrieval
Uses Aspose.Email.Pop3.Pop3Client and Pop3MailboxInfo.MessageCount API
Shows connection setup with host, port, username, password placeholders
Includes safety guard to skip real network call when placeholders detected
Wraps client usage in using block and handles exceptions gracefully
Category: Email – POP3 client operations, with placeholder safety check.

Add placeholder creation for missing appsettings.json and ensure Pop3DiagnosticLog section exists.
Use System.Text.Json to insert default EnableLogger, LogFileName, UseDateInLogFileName values.
Read those settings and apply them to Aspose.Email.Clients.Pop3.Pop3Client logging properties.
Include placeholder credential guard to skip real POP3 connections in CI environments.
Wrap file I/O and client operations in try/catch with clear error output.
Category: POP3 client configuration & activity logging.

Added safeguard before DeleteMessage execution using Pop3Client.ValidateCredentials.
Guard checks for placeholder host/username to skip CI network calls.
Uses Aspose.Email.Clients.Pop3.Pop3Client with SecurityOptions.Auto.
Ensures client is authenticated/connected before calling DeleteMessage(1).
Wraps POP3 operations in try/catch for robust error handling.
Category: POP3 client safety and credential validation.

Added POP3 email retrieval with combined subject and date filters using MailQueryBuilder.
Utilizes Aspose.Email.Clients.Pop3.Pop3Client and Pop3MessageInfoCollection for message listing.
Implements builder.Subject.Contains("newsletter") AND builder.SentDate.Since(last 7 days).
Includes safety guard: skips network calls when host/username/password contain placeholder values.
Handles credential validation and operation errors with console error output.

Added POP3 client example using Aspose.Email.Clients.Pop3
Demonstrates connecting with Pop3Client(host, user, pass, SecurityOptions.Auto)
Validates credentials then calls client.ListMessages() to fetch all messages
Applies case‑sensitive exact subject filter via string.Equals(..., StringComparison.Ordinal)
Prints UID and Subject of matching messages
Includes placeholder‑credential guard to skip real network calls in CI.

Added async POP3 client example using Aspose.Email.
Demonstrates IAsyncPop3Client with Pop3Client.CreateAsync, ListMessagesAsync, and FetchMessageAsync.
Shows asynchronous iteration over messages and printing each subject.
Includes placeholder credential check to skip real POP3 operations.
Uses SecurityOptions.Auto and CancellationToken.None for connection.
Wrapped in try/catch with proper disposal of the client.

Added example for building a MailQuery using Aspose.Email.Tools.Search.
Demonstrates MailQueryBuilder, From.Equals with case‑sensitivity flag.
Calls GetQuery() and outputs the generated query string.
Intended for POP3 client scenarios to filter messages (e.g., by attachment size).
Includes try/catch for basic error handling (safety placeholder).
No secret data included.

Added async POP3 client example using IAsyncPop3Client
Demonstrates Pop3Client.CreateAsync with SecurityOptions.Auto
Retrieves messages via ListMessagesAsync and fetches each with FetchMessageAsync
Illustrates focused async processing (e.g., printing subjects)
Includes placeholder credential check to skip real POP3 operations
Ensures proper disposal and error handling for safe execution