Mailbox unavailable. The server response was: No such user here

When you send email from an application, most SMTP servers require authentication. Your application needs to supply a valid username and password to be able to connect to the server. This prevents strangers to use your SMTP server and send millions of spam emails.

When your application does not supply the correct credentials to connect to the SMTP server, instead of a descriptive message you can get this:

Mailbox unavailable. The server response was: <> No such user here

The error message complains about the addressee, the email address you are sending the email to, instead of the username and password you try to use to access your SMTP server.

Make sure you are using the correct username and password to connect to the SMTP server.

Unable to read data from the transport connection: net_io_connectionclosed.

When your application tries to send an email using a Gmail account you may get the error message:

Unable to read data from the transport connection: net_io_connectionclosed.

One of the causes can be, when “Less secure apps” are not allowed to use the Gmail account.

To enable “Less secure apps” to use the Gmail account

  1. Log into Gmail and navigate to
  2. Select the Turn on radio button


The .NET MVC model has to have a parameterless constructor

When you create a class to be used as the model in a .NET MVC application, the class has to have a parameterless constructor. It is called during the POST when the user clicks the submit button of the form. If the class does not have a parameterless constructor, we will get the following generic error message. None of the breakpoints can help you to find the cause, and there is no entry in the event log.

The website cannot display the page
HTTP 500

Most likely causes:
•The website is under maintenance.
•The website has a programming error.

What you can try:
Refresh the page.
Go back to the previous page.
More information

Turn off the built in touchpad when a mouse is attached

All laptops today feature a touchpad, that enables you to move the pointer on the screen. It can be very annoying when your thumb accidentally moves the cursor when you type, even if an external mouse is connected to the computer.

Windows 10 provides a checkbox to automatically disable the internal pointing device when you connect a mouse.

  • Open the Control Panel,
  • Select Mouse,
  • On the Device Settings tab check the Disable internal pointing device when external USB pointing device is attached checkbox.

How to verify or generate file checksums

You can verify the checksum of a file with the built-in features of the operating systems

On Macintosh

Open the terminal window and execute the commands


shasum -a 256 FILE_NAME

On Windows

CRC32, CRC64, SHA256, SHA1, BLAKE2sp

Right-click the file in Windows Explorer and select CRC SHA > * (star)

The popup window will show the values, but unfortunately, there is no way to copy them to the clipboard.

How to upgrade TeamCity to version 10

Upgrade TeamCity to version 10

  1. Stop the TeamCity process,
    1. If TeamCity is started by a scheduled task at startup, stop the “Java(TM) Platform SE binary” process in Task Manager and disable the “teamcityserver” scheduled task in the Task Scheduler.
    2. If TeamCity is running as a Windows Service, stop and disable the “TeamCity” service,
  2. Save a copy of the TeamCity configuration directories to the data drive and an outside location
    1. D:\TeamCity\conf
    2. D:\ProgramData\JetBrains\TeamCity\config
  3. Create a backup image of your server,
  4. Create a backup of your database,
  5. Restart the box to make sure no processes hold files in the TeamCity install folder,
  6. Download the TeamCity version 10 installer from
  7. Execute the downloaded installer from the Downloads folder,
  8. If the current version of TeamCity is not installed on the C drive, make sure you select the correct location,
  9. It is not recommended to run agents on the server box. Uncheck the Windows Services and Core for the Build Agent,
  10. If you get Folder is not empty… messages, delete the files from the indicated locations and click the Retry button,
  11. Set the correct port TeamCity should to use 
  12. Select the SYSTEM account to run the TeamCity service
  13. Click the Next button to start the TeamCity service

TeamCity on 64-bit Java

The TeamCity installer also installs the 32-bit version of the Java Runtime Environment (JRE) in the “D:\TeamCity\jre” folder. To use the 64 bit Java, test if your server has  64-bit Java installed:

  1. Open a command window and execute,
    java.exe -d64 -version
  2. The installed Java is 32 bit if you get the error message:
    Error: This Java instance does not support a 64-bit JVM.
    Please install the desired version.

Switch to 64-bit Java

  1. Stop the TeamCity Windows Service,
  2. Rename the D:\TeamCity\jre to OLD_jre, so TeamCity will not find it anymore,
  3. Set the TEAMCITY_SERVER_MEM_OPTS environment variable based on the physical memory size of your server and the estimated usage
    1. minimum setting for 32-bit and 64-bit java:
    2. recommended setting for medium 64-bit server and maximum for 32-bit server:
    3. recommended setting for large server (64-bit java only):
      -Xmx4g -XX:ReservedCodeCacheSize=350m
    4. maximum settings for large-scale server use (64-bit java only):
      -Xmx10g -XX:ReservedCodeCacheSize=512m

TeamCity version 10 does not use -XX:MaxPermSize anymore.


Set up the Artifactory repository authentication

To secure Artifactory repositories follow the steps below

  1. Log into Artifactory as an administrator
  2. On the left select Admin

Add users

  1. In the Security menu select Users
  2. In the upper right select New

  3. Create users for admin, writer, and reader (REPOSITORY-NAME_admin, REPOSITORY-NAME_writer, REPOSITORY-NAME_reader)

Create security groups and add the new users to the groups

  1. In the Admin menu select Security and Groups
  2. On the Group Management page select New
  3. Create groups for admins, writers, and readers (REPOSITORY-NAME_admins, REPOSITORY-NAME_writers, REPOSITORY-NAME_readers)
    1. In the Users section add the appropriate user to the group

Create permissions and add the security groups to the permissions

  1. In the Security menu select Permissions
  2. In the upper right corner select New
  3. Create permissions to administer, write, and read (REPOSITORY-NAME_administer, REPOSITORY-NAME_write, REPOSITORY-NAME_read)
    1. Select the repository, click the green arrow to add the repository to the Selected Repositories list, and click Next
    2. Click the arrow next to the name of the group to add it to the list of groups
    3. Select the appropriate check boxes
      1. For writers select Delete/Overwrite, Deploy/Cache, Annotate, and Read
    4. Click the Save & Finish button.

To allow anonymous read access to the repository

To allow anyone to read the repository without authentication, add the anonymous user to the REPOSITORY-NAME_readers security group with Read permission.

The User Profile Service failed the sign-in. User profile cannot be loaded.

When you try to start a remote desktop connection to a Windows computer on the domain you may get the error message:

The User Profile Service failed the sign-in. User profile cannot be loaded.

To enable the User Profile update

  1. Remote into the computer with a local administrator account,
  2. In Windows Explorer open the C:\Users\Default\AppData folder,
  3. Right click the Roaming folder and select Properties,
  4. On the Security tab click the Advanced button,
  5. In the Permission entries list select System,
  6. Check the Replace all child object permissions… check box,
  7. Click the OK button,
  8. Click the Yes button on the Windows Security popup,
  9. Close the Properties window with the OK button.

Add SSH key to a Jenkins Git step

To access a Git repository Jenkins can use an SSH key.

To add the SSH key to the Jenkins server use the following Chef script

Store the SSH key in an encrypted data bag called “keys”.

 "id": "ci_private_keys",
 "ci_github_key": "-----BEGIN RSA PRIVATE KEY-----\n...\n-----END RSA PRIVATE KEY-----",


Add the following to the Jenkins Chef recipe

  • Install Git
package 'git'
  • Install the Git and Credentials Jenkins plugins
jenkins_plugin 'git'
jenkins_plugin 'credentials'
  • Copy the SSH key to the Jenkins server
rsa_key = data_bag_item('keys', 'ci_private_keys')
file '/var/lib/jenkins/.ssh/id_rsa' do
  content "#{rsa_key['ci_github_key']}"
  owner 'jenkins'
  group 'jenkins'
  mode '0600'
  • Add to the known hosts
bash 'provide RSA fingerprint' do
  code <<-EOF
   ssh-keyscan >> /var/lib/jenkins/.ssh/known_hosts
   chown jenkins.jenkins /var/lib/jenkins/.ssh/known_hosts
  not_if{system('grep /var/lib/jenkins/.ssh/known_hosts')}


To specify the SSH key in the Git step

  1. When the Jenkins server is operational, navigate to the Web interface
  2. Create a new Jenkins project
  3. In the Source Code Management section
    1. Select Git
    2. Enter the SSH URL of the repository
    3. When you are adding the first project, click the Add button to create the credential

      1. Click Jenkins to select the credentials provider
      2. Select SSH Username with private key as the Kind
      3. Enter the username you used when you created the SSH key for the Git repository
      4. Select From the Jenkins master ~/.ssh as the Private Key
      5. Click the Add button
    4. In the Credentials drop down select the credential you have created (the Git user name)


Secure passwords in TeamCity

When a TeamCity build step needs to use a password, there is a secure way to store it.

  1. In the TeamCity web interface navigate to the project,
  2. On the project page open the Parameters page,
  3. Click the Add new parameter button,
  4. Enter the name of the parameter, the password value, and click the Edit button to set the special settings,
  5. Set the Display to Hidden, and the Type to Password to hide the value from the user interface. Click the Save button on this window and the on the parent window to save the parameter.
  6. To use the parameter in a build step, surround it with % signs.