reply or forward an email having attachment, my email is seen as many attachments in another computer

the pane I posted above is the "Composing" pane. It has the top item "message format" a selector for whether the current email will be sent as Rich Text or Plain text. Try changing that and see if the email sent causes fewer complaints form your Neanderthal co-workers.

Also, under the Responding heading, there is a setting "Use the same [reply] format is the incoming format" that essentially says, "you send me plain text, I will send you back plain text."

...

There are TWO broad general ways emails can be sent: Rich Text or Plain Text. These also apply to the email READER, so if your To: is using an archaic email Reader, they will see JUNK.

• Using Rich text, formatting such as bold and underline is available, and items can be included in html code in line, not separated out.

• Using Plain text, none of that fancy formatting is available. Everything that is not PLAIN TEXT must be hung on the outside, resulting In a slew of attachments for what is TODAY considered 'ordinary' stuff inside an email.

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when are you getting this behavior and this complaint? Sending back to yourself or to someone else? does the recipient have the ability to see Rich text in their email reader?

is the reply being sent back "using same message format as received message?" <<-that can produce unexpected Plain Text.

email does not just use simple TEXT any more.

Your co-workers need to "get with the program"

=OR_

you need to make a special case just for them and convert outgoing emails to plain text before sending to them.