asp.net mailserver set up using exchange 365

We had  exchange server 2003, recently we updated MS office to MS Office 365 which there is no static IP for exchange server anymore.

We have an asp.net website which can send out emails using exchange server, the following is part of web.config file in asp.net application.

Now what should I change to make mail server work again?

<configuration>
      <appSettings>
              <add key="MailServer"  value="192.168.1.7"/>
      </appSettings>
</configuration>
HemlockPrintersAsked:
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Randy DownsOWNERCommented:
You could try the server's Internet ip that you use for your email clients. if you don't know the ip just ping it from CMD prompt.
Paul MacDonaldDirector, Information SystemsCommented:
<configuration>
      <appSettings>
              <add key="MailServer"  value="mail_server_name.domain.tld"/>
      </appSettings>
</configuration>
HemlockPrintersAuthor Commented:
There is no IP or mail server name of outlook 365 mail server
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Randy DownsOWNERCommented:
Do you have the option of setting up an email client like Outlook or confined to use webmail? If the former you will get a outgoing email server that you could use.

Your Internet Service Provider (ISP) probably provides this for you as well.

If you get the outgoing email server from your ISP or Exchange email server you can setup your application.
Scott Fell, EE MVEDeveloper & EE ModeratorCommented:
https://support.office.com/en-au/article/Outlook-settings-for-POP-and-IMAP-access-for-Office-365-for-business-or-Microsoft-Exchange-accounts-7fc677eb-2491-4cbc-8153-8e7113525f6c

Your smtp server is most likely going to be smtp.office365.com using port 587 and tls.  You may be using your own domain and the way to check is by logging into your admin manager portal for exchange.  

While logged into the admin manager panel, set  the account you are sending from and authorize remote access.  I no longer have access to office365 but that is what worked.  Check your settings in exchange to verify.

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Big MontyWeb Ninja at largeCommented:
I've requested that this question be deleted for the following reason:

Not enough information to confirm an answer.
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