ASP.NET Core + Mailexam

Minimal ASP.NET Core example that sends test mail through Mailexam SMTP via MailKit.

Based on the Mailexam ASP.NET Core guide.

What you need

• A Mailexam account and a project with SMTP credentials.
• .NET SDK 8 or newer.

From your Mailexam welcome email or dashboard:

Variable	Description
MAILEXAM_LOGIN	SMTP login (for example, xxxxx)
MAILEXAM_PASSWORD	SMTP password (paired with the login)
Host	{MAILEXAM_LOGIN}.mailexam.ru (built in Services/MailService.cs)

Quick start (host)

1. Restore dependencies:

dotnet restore

2. Export Mailexam credentials (or copy from the example file):

cp .env.example .env
export $(grep -v '^#' .env | xargs)

3. Edit .env:

MAILEXAM_LOGIN=YOUR_LOGIN
MAILEXAM_PASSWORD=YOUR_PASSWORD
MAILEXAM_PORT=587
MAIL_FROM=noreply@example.test

4. Run the application:

dotnet run

The server listens on http://127.0.0.1:8080 by default.

5. Send a test message:

curl -X POST http://127.0.0.1:8080/mail/test \
  -H 'Content-Type: application/json' \
  -d '{"to":"user@example.test","subject":"Test","body":"Hello"}'

The message appears in the Mailexam dashboard → your project → inbox.

User Secrets (optional, local)

dotnet user-secrets init
dotnet user-secrets set MAILEXAM_LOGIN YOUR_LOGIN
dotnet user-secrets set MAILEXAM_PASSWORD YOUR_PASSWORD

The example reads credentials from environment variables; export them or use CI secrets in production.

Environment variables

Variable	Required	Default	Description
MAILEXAM_LOGIN	yes	—	SMTP login; also used to build the host name
MAILEXAM_PASSWORD	yes	—	SMTP password
MAILEXAM_PORT	no	587	SMTP port (587, 2525, 465, or 25)
MAIL_FROM	no	noreply@example.test	Sender address (any test address is fine)
HTTP_HOST	no	127.0.0.1	HTTP bind address
HTTP_PORT	no	8080	HTTP listen port

For port 587 and 2525, MailKit uses SecureSocketOptions.StartTls. For port 465 it uses SslOnConnect. For port 25 it uses None.

Project layout

.
├── ASP.NET.csproj
├── Program.cs                    # Minimal API POST /mail/test
├── Services/MailService.cs
├── .env.example
├── Dockerfile                    # for local debugging only
└── docker-compose.yml

Docker (debugging)

Docker is provided for local debugging. For day-to-day development, run the app on the host with dotnet run (see above).

cp .env.example .env
# edit .env with your credentials

docker compose up --build

Then call the same endpoint on the mapped port:

curl -X POST http://127.0.0.1:8080/mail/test \
  -H 'Content-Type: application/json' \
  -d '{"to":"user@example.test","subject":"Test","body":"Hello"}'

Inside the container the server binds to 0.0.0.0:8080.

CI

Set these secrets in your CI environment:

variables:
  MAILEXAM_LOGIN: $MAILEXAM_LOGIN
  MAILEXAM_PASSWORD: $MAILEXAM_PASSWORD
  MAILEXAM_PORT: "587"
  MAIL_FROM: "noreply@example.test"

After sending a message in a test, verify delivery via the Mailexam API.

Troubleshooting

TLS or authentication failed

• Host must be {login}.mailexam.ru, where {login} matches MAILEXAM_LOGIN.
• Login and password must come from the same Mailexam project.

Port 587

• Use SecureSocketOptions.StartTls, not SslOnConnect.

Message not in the dashboard

• Open the inbox of the same Mailexam project.
• Enable verbose logs in appsettings.Development.json if needed.

See also

• Mailexam ASP.NET Core guide (wiki)
• Spring Boot reference implementation — SMTP on JVM
• MailKit documentation
• Mailexam API documentation