Add ability to disable POP3 and IMAP servers via null port configuration

[Copilot]

POP3 and IMAP servers now consume ports even when unused. Users need the ability to disable them independently.

Changes

• Pop3Server.cs: Early return in StartAsync() when Pop3Port is null (matching existing IMAP behavior). Fixed ListeningPorts to return empty array when disabled instead of defaulting to port 110.

• appsettings.json: Document that null port values disable servers.

• CommandLineParser.cs: Update help text to show empty string disables servers.

Usage

Command line:

smtp4dev --pop3port="" --imapport=""

Config file:

{
  "ServerOptions": {
    "Pop3Port": null,
    "ImapPort": null
  }
}

Environment variables:

export ServerOptions__Pop3Port=
export ServerOptions__ImapPort=

Disabled servers log: [INF] POP3 server disabled - no port configured

Default behavior unchanged - both servers remain enabled by default.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Ability to disable POP3</issue_title>
<issue_description>POP3 is new to v3.11.0. I'd ask for the ability to disable it, since if one uses IMAP, it's not always necessary but uses a port. Possibly, others would be interested in similarly disabling IMAP.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Ability to disable POP3 #1997

---

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[github-actions]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[rnwood]

📊 Code Coverage Report

Coverage Type	Percentage	Status
Line Coverage	14.3%	🔴
Branch Coverage	4.9%	🔴
Method Coverage	17.6%	🔴

📁 Coverage by Namespace

Namespace	Line Coverage	Branch Coverage	Method Coverage	Classes
LumiSoft.Net	0% 🔴	0% 🔴	0% 🔴	23
LumiSoft.Net.AUTH	0% 🔴	0% 🔴	0% 🔴	18
LumiSoft.Net.IMAP	1.7% 🔴	0.4% 🔴	3.9% 🔴	122
LumiSoft.Net.IMAP.Client	0% 🔴	0% 🔴	0% 🔴	8
LumiSoft.Net.IMAP.Server	0% 🔴	0% 🔴	0% 🔴	25
LumiSoft.Net.IO	0% 🔴	0% 🔴	0% 🔴	13
LumiSoft.Net.Log	0% 🔴	0% 🔴	0% 🔴	3
LumiSoft.Net.Mail	0% 🔴	0% 🔴	0% 🔴	14
LumiSoft.Net.MIME	0% 🔴	0% 🔴	0% 🔴	41
LumiSoft.Net.TCP	0% 🔴	0% 🔴	0% 🔴	6
LumiSoft.Net.UDP	0% 🔴	0% 🔴	0% 🔴	3
Rnwood.Smtp4dev	1.9% 🔴	3.3% 🔴	12% 🔴	14
Rnwood.Smtp4dev.ApiModel	58.5% 🔴	54.5% 🔴	44.3% 🔴	17
Rnwood.Smtp4dev.Controllers	3.5% 🔴	4.7% 🔴	9.2% 🔴	11
Rnwood.Smtp4dev.Data	55.6% 🔴	40.9% 🔴	60% 🟡	3
Rnwood.Smtp4dev.DbModel	72.1% 🟡	0% 🔴	67.3% 🟡	6
Rnwood.Smtp4dev.DbModel.Projections	100% 🟢	0% 🔴	100% 🟢	1
Rnwood.Smtp4dev.Hubs	0% 🔴	0% 🔴	0% 🔴	1
Rnwood.Smtp4dev.Migrations	90.2% 🟢	0% 🔴	71.7% 🟡	23
Rnwood.Smtp4dev.Server	15.4% 🔴	14% 🔴	20.3% 🔴	15
Rnwood.Smtp4dev.Server.Imap	84.8% 🟢	85.3% 🟢	78.9% 🟡	2
Rnwood.Smtp4dev.Server.Pop3	76.1% 🟡	65.2% 🟡	96.8% 🟢	2
Rnwood.Smtp4dev.Server.Pop3.CommandHandlers	48.3% 🔴	26.1% 🔴	84.6% 🟢	12
Rnwood.Smtp4dev.Server.Settings	67.1% 🟡	16.7% 🔴	72.1% 🟡	10
Rnwood.Smtp4dev.Service	0% 🔴	0% 🔴	0% 🔴	5
Rnwood.Smtp4dev.TUI	0% 🔴	0% 🔴	0% 🔴	9
Rnwood.SmtpServer	72.1% 🟡	63.2% 🟡	68.3% 🟡	36
Rnwood.SmtpServer.Extensions	67.9% 🟡	25% 🔴	91.3% 🟢	6
Rnwood.SmtpServer.Extensions.Auth	59% 🔴	47.6% 🔴	57.5% 🔴	23
Rnwood.SmtpServer.Verbs	92.9% 🟢	92% 🟢	100% 🟢	12

Overall Coverage Details:

• Covered Lines: 5983 / 41714
• Covered Branches: 587 / 11973
• Covered Methods: 701 / 3973
• Assemblies Tested: 3
• Total Classes: 484

📈 View Full Coverage Report

Enhanced coverage report with namespace breakdown - Azure DevOps Build #3.12.0-ci20251228104_pr1998 20251228.5