How can I send an audio file online through email as an attachment?

Zip it and attach.

This is assuming you are on windows (xp or newer)

Right click the audio file. Select SEND TO > COMPRESSED FOLDER

Once complete, right click the NEW audio.zip file
Select SEND TO > MAIL RECIPIENT

OR

Start a new email, drag drop the zip file into the body

OR

Start a new email, insert > file, then select the new zip

:)

zip it and attach.

this is assuming you are on windows (xp or newer)

right click the audio file. select SEND TO > COMPRESSED FOLDER

once complete, right click the NEW audio.zip file
select SEND TO > MAIL RECIPIENT

OR

Start a new email, drag drop the zip file into the body

OR

Start a new email, insert > file, then select the new zip

:)

The above process assumes the file is on the local machine, however, unless I misunderstood the OP, the file resides on the internet. Therefore, the file would have to be saved to the local machine prior to the above mentioned steps taking place. Keep in mind, depending on where you're getting the file from, DRM copyrighted material once downloaded can not normally be sent through email.