Category Archives: Tutorials

Exchange Microsoft Tips & tricks Tutorials Utils

How to prevent internal email spoofing in an Exchange organization

Ensuring email security might be one of the most important and most difficult tasks an administrator must face. Every day, servers process thousands of emails and controlling such a big mail flow is not easy. No wonder hackers focus on this channel when they plan attacks. They use various tricks to make users think that opening a suspicious attachment is a good idea.

One of the tricks they use is email spoofing.

Prevent Internal Spoofing in Exchange organization

What is email spoofing?

Email spoofing is a very popular attack method. The sender modifies message headers so that emails appear as sent from someone else. Hackers use it, for example, to impersonate employees of a company to obtain login credentials, personal data, or other confidential information. Two most common ways to protect your organization from external spoofing attacks are:

  • An SPF record – a list of IP addresses which are authorized to send emails from a domain.
  • DKIM check – an email authentication method. It enables you to sign and verify email messages using public and private keys. The public keys, published in the DNS records are used to verify if the message comes from the original sender. You cannot configure it on the Exchange Server natively – you require a plugin for SMTP gateway.

Both ways give good results when fighting with external spoofing. The problem starts when we come across internal spoofing when one employee tries to impersonate a colleague. It might be a joke, or to achieve some benefits – either way, it can sabotage a company in a number of ways:

  • Cause chaos,
  • Induce material damage,
  • Harm data integrity,
  • Damage the company reputation.



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Networking Tutorials Utils

Nmap Cheat Sheet

Nmap has a multitude of options and when you first start playing with this excellent tool it can be a bit daunting. In this cheat sheet you will find a series of practical example commands for running Nmap and getting the most of this powerful tool.

Keep in mind that this cheat sheet merely touches the surface of the available options. The Nmap Documentation portal is your reference for digging deeper into the options available.

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Exchange Tutorials

550 5.7.1 Message rejected as spam by Content Filtering

Content Filtering has been enabled on the recipients’ mail server. This configuration is incompatible with GFI MailEssentials when installed as a relay server, all email filtering should happen on the relay server. For more information on Content Filtering and how to disable it, please see the following:

If the mail server is Microsoft Exchange 2013 and 2016 server:

If the mail server is Microsoft Exchange 2010 server:

If the mail server is Microsoft Exchange 2007 server:



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Imports FreeTextBoxControls
Partial Class _Default
Inherits System.Web.UI.Page

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim toolbar1 As New Toolbar()
toolbar1.Items.Add(New ParagraphMenu())
toolbar1.Items.Add(New FontSizesMenu())

Dim toolbar2 As New Toolbar()
toolbar2.Items.Add(New Bold())
toolbar2.Items.Add(New Italic())
toolbar2.Items.Add(New Underline())
toolbar2.Items.Add(New ToolbarSeparator())
toolbar2.Items.Add(New BulletedList())
toolbar2.Items.Add(New NumberedList())
End Sub
End Class

propriedade ToolbarLayout:

ParagraphMenu, FontFacesMenu, FontSizesMenu, FontForeColorsMenu
,  FontForeColorPicker, FontBackColorsMenu, FontBackColorPicker
, Bold, Italic, Underline, Strikethrough, Superscript, Subscript
, InsertImageFromGallery, CreateLink, Unlink,  RemoveFormat
, JustifyLeft, JustifyRight, JustifyCenter, JustifyFull
, BulletedList, NumberedList, Indent, Outdent, Cut, Copy, Paste
, Delete, Undo, Redo, Print, Save,  ieSpellCheck, StyleMenu
, SymbolsMenu, InsertHtmlMenu, InsertRule, InsertDate, InsertTime
, WordClean, InsertImage, InsertTable, EditTable, InsertTableRowBefore
,   InsertTableRowAfter, DeleteTableRow, InsertTableColumnBefore
, InsertTableColumnAfter, DeleteTableColumn, InsertForm, InsertForm
, InsertTextBox, InsertTextArea,  InsertRadioButton, InsertCheckBox
, InsertDropDownList, InsertButton, InsertDiv,  InsertImageFromGallery
, Preview, SelectAll, EditStyle.


Nota: Se você for usar o componente para enviar mensagens não esqueça de desabilitar o ValidateRequest definindo na página ASPX o seu valor como false:

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" validateRequest="false" %>

Code Snippets Microsoft Networking Tutorials

How to find a Global Catalog server?

With DNS Requests (NSLOOKUP)

In an Active Directory environment, all Global Catalogs are anchored in DNS . There is a separate subdomain ‘GC._msdcs ….’ in the namespace of the AD root domain (please remember: the global catalog does not refer to individual domains, but to the entire forest). So if your root domain in the forest is e.g. example.root, then you get a list of all GCs with this command:

C:\> nslookup gc._msdcs.example.root

Server:  dns01.example.root

Name:  gc._msdcs.example.root

The container _msdcs contains the infrastructural DNS records of the Active Directory. This is also where all the SRVservice records for the domain controllers are stored.


You can also use the standard command line tool DSQUERY for searching GCs. The search can be limited to certain domains or AD sites. However, you must be authenticated in the regarding forest and DSQUERY must be available on your machine (this is usually the case on Widows servers). As a result, the server objects in the Configuration partition is displayed:

C:\> dsquery server -isgc


C:\> dsquery server -isgc -domain ""

C:\> dsquery server -isgc -site "Site-Auckland"

Per Script with an LDAP filter
In the last section we have seen that the global catalog servers are present in the configuration partition of the directory as specific objects. Her we can look for them with our own script. These servers have set the first bit in their ‘options’ attribute. All we need is the appropriate LDAP filter:

ldapFilter = "(&(objectClass=nTDSDSA)(options:1.2.840.113556.1.4.803:=1))"

Set rootDSE = GetObject("LDAP://rootDSE")
configDN =   rootDSE.Get("configurationNamingContext")

Set ado = CreateObject("ADODB.Connection")
ado.Provider = "ADSDSOObject"
ado.Open "ADSearch"
Set objectList =   ado.Execute("<LDAP://" &configDN& ">;" & ldapFilter & ";distinguishedName;subtree")

While Not objectList.EOF
nTSDSA = objectList.Fields("distinguishedName")
serverDN = Mid(nTSDSA, 18)                                         'CN=NTDS Settings abschneiden => Server Objekt
Set serverObj = GetObject("LDAP://" & serverDN )

WScript.Echo serverObj.dNSHostName




Tutorials Utils VB Visual Studio

Default certificate could not be created. Publish aborting

You need to tell the Publisher where to get the Certificate from:

  1. Go to Project-> Properties
  2. Go to the tab named “Signing”
  3. Check the Checkbox labeled ‘Sign the ClickOnce manifests’. This enables the section where you can point to a certificate.
  4. Click on the button labeled ‘Select From File…”. In the directory listing, choose a key file (.pfx) and Open.
  5. From the step 3, click the button labeled “More Details…”. This will display the certificate you’ve just selected.
  6. Click “Install Certificate” and follow the prompts.
  7. Save and Publish your Solution.
Tips & tricks Tutorials

Erro 105 (err_name_not_resolved)

Erro 105 é um erro chato que às vezes você encontrar ao usar o Google Chrome. Na realidade, este erro não é um problema com o Chrome, mas é um problema com a sua conexão com a internet e as configurações de DNS. Siga as instruções deste tutorial para corrigir o problema rapidamente.

Erro 105 é um erro de conexão que pode aparecer quando você estiver usando o Google Chrome. Ele pode aparecer a qualquer momento e não é causada por um determinado site. Quando você encontrar erro 105, você também vai ver a seguinte mensagem exibida:
erro 105 (net::err_name_not_resolved): não foi possível determinar o endereço dns do servidor.
Por que erro 105 aparecem no Chrome?

Há várias razões para erro 105 aparecerá. Eles estão todos relacionados com a configuração de sua conexão de internet e como o seu computador acessa a internet. É muito técnico, mas, essencialmente, o problema é causado pela forma como o computador está tentando se conectar à internet. Ele pode ser bloqueada pelo firewall ou pelo seu ‘router’.

Como corrigir o erro 105?

Existem três métodos para a fixação de erro 105. A melhor solução é alterar as configurações do Google Chome, que é bastante fácil de fazer (solução 2). Os outros dois envolvem redefinir algumas das suas conexões de internet e também verificar o seu regras de antivírus/firewall.
Solução 1
Esta solução irá repor o catálogo Winsock de volta para a configuração padrão. É seguro.
1. Abra o aplicativo cmd (prompt de comando),  Basta clicar no botão do Windows, digite cmd, Botão do Windows 7
2. Isto irá abrir uma janela preta Prompt de comando
3. Tipo: netsh winsock reset catalog
4. Pressione a tecla ENTER
5. Tipo: netsh int ip reset reset.log
6. Pressione a tecla ENTER
7. Reinicie o computador

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Tips & tricks Tutorials

Speed comparison between USB 2.0, USB 3.0, SATA and Firewire

The theoretical maximums are as follows:

In bits per second, that is:

  • USB 1.1 = 12 Mbit/s
  • Firefire 400 = 400 Mbit/s
  • USB 2.0 = 480 Mbit/s
  • FireWire 800 = 800 Mbit/s
  • USB 3.0 = 5 Gbit/s
  • USB 3.1 = 10 Gbit/s
  • eSATA = Up to 6 Gbit/s (750 MB/s) right now as it depend on the internal SATA chip.
  • Thunderbolt = 10 Gbit/s × 2 (2 channels)
  • Thunderbolt 2 = 20 Gbit/s
  • Thunderbolt 3 = 40 Gbit/s

In Bytes per second, that is:

  • USB 1.1 = 1.5 MB/s
  • Firefire 400 = 50 MB/s
  • USB 2.0 = 60 MB/s
  • FireWire 800 = 100 MB/s
  • USB 3.0 = 625 MB/s
  • USB 3.1 = 1.21 GB/s
  • eSATA = 750 MB/s
  • Thunderbolt = 1.25 GB/s × 2 (2 channels)
  • Thunderbolt 2 = 2.5 GB/s

However, this does not provide the actual answer. As an example, FireWire 400 is a serial connection. The entire 400 Mbps is available for data transfer. USB 2.0 sends command and control data through the same connection the data uses limiting the 480 Mbps connection to 380 to 400 Mbps. When considering throughput the list looks entirely different.

Tips & tricks Tutorials

IP Ratings (Ingress Protection)

IP_Code_ProtectionTwo-digit number established by the International Electro Technical Commission, is used to provide an Ingress Protection rating to a piece of electronic equipment or to an enclosure for electronic equipment.

The protection class after EN60529 are indicated by short symbols that consist of the two code letters IP and a code numeral for the amount of the protection.

Example: IP65 (NEMA 4)
The two digits represent different forms of environmental influence:
• The first digit represents protection against ingress of solid objects.
• The second digit represents protection against ingress of liquids.

The larger the value of each digit, the greater the protection. As an example, a product rated IP54 would be better protected against environmental factors than another similar product rated as IP42.

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Tips & tricks Tutorials

Break lines at specific character in Notepad ++

  1. In Notepad++, click Search > Find.
  2. Click the Replace tab.
  3. Under the Search Mode group, select Regular expression.
  4. In the Find what text field, type ],\s*
  5. In the Replace with text field, type ],\n
  6. Click Replace All.

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