Let's break the implementation down into multiple steps. For the basic implementation, we want to keep a list of emails in your component's state, and when rendering, render a textbox for each email from this list. This will enable us to then easily add and remove textboxes by simply manipulating the DOM itself. For convenience, you can supply each textbox with an additional attribute that stores its index, although it is also possible to calculate this dynamically. At the end, you can render an additional textbox with placeholder text to enter the next email address. This will ensure that there is always at least one textbox (especially at the start before any data is entered), and that the user always has somewhere to type. The index of this placeholder textbox should be N, where N is the number of elements in the email list.

Next, you need to handle the onChange event for each of your textboxes. Here, you should check if the text is empty, and if so, delete the email corresponding to the index of the textbox from your list. Otherwise, update it to the new value to ensure consistency. When you remove an email, you should also focus the placeholder textbox for better usability.

Then we need to handle entry of characters into the placeholder textbox. As soon as the first character is entered into the placeholder textbox, instead of displaying there, you should intercept the event and add an additional entry to your email list. Focus the new textbox so that the remaining input goes there instead, while keeping the placeholder textbox empty. This gives the user the impression that the placeholder textbox turned into a regular textbox and a new placeholder textbox popped in below.

The last implementation detail is pasting a list of emails. To do this, intercept the onPaste event in the placeholder textbox. Keep in mind that you cannot rely on each system using the same line terminators. As such, since emails cannot contain whitespace, you should simply split the pasted content on whitespace characters. Optionally, you can check the emails you get for validity, and then add all the valid emails you have parsed to the email list in your component state. This will then make React create the required textboxes automatically, as with manual input.

One small detail that we need to address is validation. Contrary to popular belief, valid emails are not entirely trivial to validate. However, there exists a regular expression that correctly verifies virtually every email that adheres to standard conventions, namely ^(([^><()[\]\\.,;:\s@"]+(\.[^><()[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))
You can use this expression to do your validation.



There are many different possibilities to answer this question. We will go top down beginning with the browser.
Most of the browsers support the html input tag of type "email" and most of them would automatically warn the user about a wrong format of the address. However there are many standards of email address pattern. Furthermore the user might disable the browser validation, so we should not rely on this.
The second station is the javascript of the browser. Probably the easiest way to validate the email address is to use a regular expression an match the input against this expression. However the user may disable the javascript or send a request in other way than browser. Therefore it's absolutely necessary to validate the email address on the server side. This might be done by a regular expression, but some more sophisticated systems would check the MX record of the domain given in the email address, to be sure it might be a real address of a real mail server.




Encrypting and decrypting emails by S/MIME

1. Configure mail application for example Thunderbird. S/MIME does not work in the browser.
2. Generate your public and private key using for example ssl or extension to your mail application.
3. Create a certificate signing request using for example ssl.
4. Send request to "third Party" authority. There are many free and payed authorities, however the second ones are more trustworthy.
5. Download signed certificate and certificate of the authority.
6. Import signed certificate and certificate of the authority to mail client.
7. Now you can sign your emails by the certificate.

Use "GoAnywhere OpenPGP Studio" to secure email communication

Open PGP is the preferred standard for most banks and financial institutions when transferring sensitive data.
Open PGP is a form of asymmetric encryption where a public key is used to encrypt the file and a corresponding private key is used to decrypt the file. Several encryption algorithms can be utilized within Open PGP, including the Advanced Encryption Standard (AES), to provide a high level of protection. Digital signatures can also be used to sign files to allow the recipient to authenticate the validity of the sender's signature.

"GoAnywhere OpenPGP Studio" can be used as follows for generating public/private key pair, for exporting public keys and for encryption/decryption of sensitive data:

1) Download and install GoAnywhere OpenPGP Studio from

2) Recipient creates new private/public key pair
- Download and install "GoAnywhere OpenPGP Studio".
- choose "OpenPGP Keys" tab
- click "Create" button to generate new key
- enter the required information and click the create button

3) Recipient exports public key
- choose "OpenPGP Keys" tab
- select the key you want to export
- click "Export Public Key(s)"
- choose location where to store the public key

4) Recipient sends the exported key to a person from whom you would like to receive encrypted emails

5) Sender encrypts file
- choose "OpenPGP Tasks" tab
- navigate to the file you want to encrypt and mark it
- click the "Encrypt" button
- choose the key with which you want to encrypt and specify the location where to store the encrypted file
- click the "Ok" button

6) Sender sends the encrypted file per email

7) Recipient decrypts the encrypted file
- choose "OpenPGP Tasks" tab
- navigate to the file you want to decrypt and mark it
- click the "Decrypt & Verify" button
- choose a location where to store the encrypted file

Encrypt email attachment with PGP

Privacy on the Internet is a growing concern, especially as more and more people are using it for their professional and personal business, socializing, and entertainment. Information sent over the internet or by email is not necessarily secure. You don't know how many servers the message will pass through between your computer and the recipient's, or who has access to those servers.


example of a smtp dialog

Connect to an arbitrary mail server on port 25 using telnet
telnet 25

The mail server responds
Connected to
Escape character is '^]'.
220 ESMTP Postfix (Ubuntu)

Type into the smtp session:

The mail server responds:
250-SIZE 40960000
250 DSN

Tell the mail server who is the sender:
250 2.1.0 Ok

Tell the mail server who is the recipient:
250 2.1.5 Ok

Tell the mail server that you want to deliver the actual data:
354 End data with .
Subject: test
Hello World!

Quit your message by using a single dot

250 2.0.0 Ok: queued as 13C248D49E5D

Quit the SMTP session
221 2.0.0 Bye
Connection closed by foreign host.


How to test a mail server?

Which steps have to be done to manually send an email using the SMTP protocol? This can be useful to check after setup if a mailserver is configured properly.


Reject virus messages using Postifx

The Postfix mail server is in place to received and send emails. To improve security incoming and outgoing messages should be scanned for malware. If the scanner detects a virus, Postfix should be reject the message in order to prevent users from receiving malware.

How to send an eMail via PHP?

The core problem of this challenge is to find an existing PHP-function, which enables a programmer to send an eMail. Furthermore, the correct syntax and the required data of the mail-function is an essential problem.

Login at a website without having to registrate

You want to do a login at a website, but you do not want to registrate at the website (for example you do not want to have to wait for an activation of your account, you want to login instantly, you do not want to give your email address to another possible spammer, you only want to login once, etc. )


Subscribe to email