There can be many reasons why anyone would want to send an anonymous mail that can’t be traced back to the original sender. It could be something secret between two people or among some persons of any organization, or it could be investigative blogging and reporting. If you want to send an anonymous email, here are some good methods:

Use VPN for anonymous emails​

You can use VPN (Virtual Private Network) to send material to someone in a way that can’t be traced back. When you use a VPN, you are already using a different IP address. But your mail ID will identify you.

Use Burner email accounts​

Burner email accounts allow you to create a random email ID so that you can enter it on websites when browsing. This way, everything on the Internet who asks for your IP address, gets a fake IP address. Using burner mails to sign up and verification can help you stay away from spam. The burner email ID can be connected to your real email account so that any mail that reaches your burner email accounts is transferred to your real mail ID.

Create a disposable email account​

If you intend to use the burner email only once, it is better to create a disposable email ID as the latter can be set to self-destruct after a period of time. Please note that the burner email ID is different from disposable mail accounts. The burner mail accounts can be used for longer compared to disposable email accounts. The disposable mail accounts can be set to self-destruct as soon as any incoming mail is read. Or the person using disposable mail ID can simply set a timer so that the mail ID is disposed of after a certain time.

How to send an anonymous email to somebody
The following are some websites that allow you to to send an anonymous mail to somebody free that can’t be traced:

Temp Mail – Disposable Temporary Email​

You can send an mail using temp-mail.org. You may use it for things like mail-verification upon signups. You can later delete the entire email address and its content without having to receive further emails from sites where you used the temporary mail.
You do not have to create an account. You don’t have to provide data about yourself. You simply type the mail content and then enter the destination email address to send mail.

Guerrilla Mail – Disposable mail ID​

GuerrillaMail.com helps in sending anonymous messages anywhere, to anyone, in this world. This is actually a disposable mail ID provider.
You can create a disposable mail ID by selecting the server using the drop-down menu. In the text box preceding the server name, you can enter an ID that is going to be cleaned every hour.
There is a Scramble Address option available so that you can convert your mail ID to random characters so that it becomes difficult for the receiver to trace you and the origination of the mail you sent.
You don’t have to provide any details about yourself. Allemails in Guerrilla Mail are deleted after one hour of reaching the inbox.

AnonEmail Email Account​

The AnonEmail is short for Anonymouse.org. You need not provide any information to use this service. It can be used for outgoing emails only. Simply fill in the target destination mail, type a subject for the mail, type the mail, and then click on Send Anonymously button.

Send Anonymous mail​

SendAnonymousEmail.net is another free service that lets you send anonymous emails. I have tested it and it works.

Anonymous mail​

Anonymousemail.me is similar to the AnonEmail listed above. It’s plus point is a “Reply-To” address to which you can direct any replies. A Premium plan is also available that allows sending unlimited emails along with tracking features.

The free plan allows you to access the fields “To”, “Subject”, and “Compose” text box as seen in the image. The free plan allows up to three attachments.

Mailnesia – For incoming mail​

Mailnesia.com is also a quick set up inbox for receiving website sign up notifications. For example, you need to enter a valid email for accessing certain artefacts from the web. You can quickly create a Mailnesia inbox.