In the new user registration page, how to check whether the email id entered by a user is valid? I want to check the entered email id actually exists before the user submits his information. Please do not give code for checking email id string using regular expression, I want to check whether the entered email id actually exists.
You can not "check" that reliably. You need to "ask", send an email to that address with a secret code that your users must enter on your site, or a link with the secret code that the user must click.
Edit: About the reliably part.
While an SMTP server may respond that a mail address is invalid they usually don't, because that would help spammers identify valid addresses more easily. That would also require your code to talk directly to the SMTP servers responsible for each domain. Usually you send mail though your local SMTP server that does the job of forwarding the mail to the right recipient(s).
What you can do however is at least check that the domain exists by asking your favorite DNS service.
In order to do this, you'd need to telnet to the email provider in order to check if it exists. Hotmail, for one, will not allow you to do this.
You should be using membership system for your ASP.net registration form.
Here is a good article explaining how it all works:
https://web.archive.org/web/20211020202857/http://www.4guysfromrolla.com/articles/120705-1.aspx
Including a page on how to verify email addresses like you describe
The only 100% accurate method is to send it an email and ask the user to click a link in that email to complete registration.
Short of that, there is a falible method of connecting to the mailserver. I'll see if I can find a good article(here you go) and edit this post with a link shortly.
This depends on the email provider. most of the providers block this option to prevent spammers from knowing which address is valid...
Related
Is there any mechanism in which you can prevent a user from replying to an email message? Here's the use case:
An automated system (C#.net) sends emails to a user. The action of the task
is included in the email message (e.g. RSVP link for "yes" or "no")
Instead of using the buttons/actions in the email, the user replies
to the email.
The email originally sent specifically says that the mailbox in use
is unmonitored. (in bright red box!!!)
The user doesn't actually read the email, and gets pissed off when nobody replies or his RSVP is "lost"
Clearly a user issue. I'm thinking the best recourse might be an automated reply saying the mailbox is unmonitored if a user replies to the e-mail.
Any SMTP conditions/flag which can prevent a user from replying in the first place?
I don't believe there is any setting that you can include in the original email that would stop someone from replying to an email.
If the recipient really wants to reply, they can literally copy-paste the sender's email address into a new email and reply to it that way.
Just wanted to point out that the following hack is not elegant and would result in a bad customer experience. This is the only way I could think of achieving this.
One hack that comes to my mind is that you can try to set MailMessage.ReplyToList property to an invalid email address like - abc#g#g.com. In theory, this will force the customer's email client to reply to the invalid email address instead of the original sender. We can hope that the customer's email client validates that before sending the reply.
I have not tried this myself as I don't have an SMTP server to validate. But if the SMTP server does not validate the ReplyToList value then it should work.
Again this is a super sketchy hack and might not work with all the email clients out there.
You are better off setting up an auto-reply on the mailbox.
I have a form in my asp.net site. when user fills email id text box, I want to make sure whether that email id is valid or invalid(existing or not existing).
Ex: john#gmail.com is valid,
john#xxxyyy.com is not valid.
How to find it whether it is valid or not. please help me. I searched some stack overflow. even though I didn't get.
There is no way to for you to know if an email account actually exists other than to send an email and see what happens. A delivery failure notice might be sent, but that is not guaranteed to be sent, and even if it is, it might not be sent for days depending on how many delivery attempts are made.
You can send a verification email which contains a URL of a web service you control and passes a unique ID. The email owner clicks on the URL and is directed at your web service. You look at the unique ID and now you know the email address exists.
https://emailhunter.co/api/docs#email-verification - is a web service API to check email addresses
try to create an email id in mail server. if exist it will return an existing mail return message.
You could use the built-in Microsoft SmtpClient Class if you know the adress of your SMTP server. The Send Method returns an exception when the delivery fails. Again, this is only a suggestion and perhaps too overwhelming for what you need, but this class is rather useful in C#.
Send one link on that email address with some query string parameters and based on those parameters activate their user profile otherwise not activate..
So based on this methodology, you can verify email address is valid or not.
I want to add this feature to my application. It works OK but I'm afraid of a problem here. At first, I'll talk a little about how I implement the feature. Simply, the user has to register his email address first (at the registration time). If he loses his password, he can click on a link to activate the sender. This sender will send the password (corresponding to his username) to his registered email address. I think there should have many kinds of sender here and I'm using SmtpClient to send the email. This Smtp needs a NetworkCredential, and I provide it with some valid and active Credential. I have to create some user accounts (in Gmail and Yahoo networks), apply these accounts information as the credentials for my Smtp.
Here is the problem, my Password restoring feature won't work if all those credentials being invalid or inactive. I mean if all the user accounts (I created in Gmail and Yahoo mail) somehow are inactive, the Smtp will be unable to send the email. The most popular reason for those accounts being inactive is there hasn't been any access/login to them for a long time (e.g: about 3 months) It is almost certain that it will happen, except I have to remind myself to login to those accounts periodically to keep them active.
I wonder if there is any solution for this? I've thought of keeping those accounts information in a config file but the customer won't know how to edit that config file to change the sender credential information and even they know how to, that's so inconvenient. I've also thought of popping up a window requiring information for the sender credential from user (user may use his own email account or has to create a new one), it's also inconvenient, I think so. I've also think of logging to those accounts (via my application) periodically (about once a month) to keep them active. But I wonder if there is a better solution, plus that requires the user computer to be connected to Internet and this is not always met (even there is a situation that the user computer is always off line for months or years, but suddenly one day, he loses his password, he wants to get it back and at that time, he connects his computer to the Internet and uses the password restoring feature, but he can't because all the accounts built-in for the sender credentials has been inactive because of not having any access/login to them for months/years).
Do you have any idea on how to solve this problem?
UPDATE
I'm sorry to who suggested me that there is a security flaw here but I just want a solution for the password restoration. If you are kind enough please let me know what the security flaw is in detail. As I mentioned above, there is of course a security flaw because of the user password (a plain text) is saved in memory. But that's just a demo and it's only for demonstrative purpose for my real problem which is sending the user a new password (or any kind of authoritative access info). Here is what I want to explain more:
Suppose user's password is: Iloveprogramming
After hashed, it should be 3920bdbd4c000dd392e2501e89747173
That's all my application knows about user's access info.
When user typed in his password correctly, that entered password should be hashed into the same string above and this will be compared against the hashed string stored in the database and he should be logged in.
Now if he forgets his password, What can I do?
Here is the way most of websites do for us (who unfortunately forget our passwords):
- Support a link like "Forgot your password?"
- Clicking the link will lead you to a page like this:
-> Supply your user name: ............
-> Click OK (or any submit button) to get your new password.
I would like to do the same with my application. This is a windows forms application. I know that the content sent to the user email address should only be some confirmation link (about the password restoration), not a password (this is known only by the user who uses the email the password is sent to, however other users may disturb him by clicking on the 'Forgot password' link and fill in his user name). But it is only a must-do for a multi-user application, my application is in fact for only 1 user using on his own machine. What is the flaw?
Here is what I intend to do:
Auto-Generates the password, hashes this password and saves that hashed string into the database as the new hashed password for him. After that, send this auto-generated password immediately to his email address.
Dispose the string which stores the newly generated password.
What is the flaw here? And if it does exist, please let me know another solution for this? I'm just afraid of the email account which is used to send the password to my user's email address may not work (inactive) in future for some reason (as I said, not logging in for a long time).
Please feel free to explain the flaw detail in an answer, it may not answer to my original question but it does help me and I would accept that answer. Thank you!
Again, I don't have money for a dedicated website for the password restoring feature of my winforms application.
I am checking the validation for email using regular expression its working fine for me. What if the user give some dummy mailid in the textbox?
How can i check whether the entered mail is valid or not without telling the user to login to that mail and click subscribe link?
Is it possible to check like this..
Thanks in advance
How can i check whether the entered
mail is valid or not without telling
the user to login to that mail and
click subscribe link?
You can not. Point. Thanks to spammers no email server wil lbehave. Some will send you "user doesn ot exist" errors, some will even swallow them.
Plus, legally, youalso have to make sure the subscriber actually OWNS the mailbox, and is not entering someone else email.
The only way which i think is
Send an email to the specified email address , if you don't got a bounced email , email is valid provided by user
Without verifying that the user can actually read email, you can't ensure it's that user's real account.
Many domains accept all mail, and use it for spam analysis on invalid accounts, and a user can easily provide 'real' accounts they don't control. (eg: sales#example.com)
Really sorry because this is almost "please send me the code" - although really it's "please send me a link to another discussion"
I am setting up a .net membership system and need to validate users from the email address they provide via a "click here to validate your account" type link.
Just wondered if anyone knew of any good tutorials or posts out there about this? I have searched for about an hour and can't find anything - hence me asking the question.
Thanks in advance.
Rob
This is very easy, once they submit their application form, log a "token" variable, dispatch your email, add the token variable to the url, search for the token in the db, validate user...!! Simple.
When they are registering send them a hash of some of their data with a fixed salt. Stuff like time of registration and user-id. When they click the email link to something like /verify?q=ahash, just check to see which users data the hash amounts to, and update the database to reflect that they are a valid user.