[OT] Has my e-mail account been hacked?

[Stephen Powell <zlinuxman@wowway.com>]

About a week ago, I discovered hundreds of "mail delivery failure"
messages in my inbox.  Investigation revealed that they were all for
SPAM e-mails that I did not send.  I am guessing that this means one
of two things:

(1) Someone discovered my password somehow, logged into my ISP
account as me, and sent out a bunch of SPAM.

Or

(2) Someone sent out a bunch of SPAM, spoofing my e-mail address
as the sender, and the delivery failures came to me.

How can I tell which is the case, and if it's (2), is there anything
I can do to defend myself against this sort of thing in the future?

(I do know enough not to respond in any way to the almost-daily phishing
attacks that try to get me to supply my userid and password.  I have
never responded to any of them.)

I am running Debian stretch; but of course I realize that this question
is not, strictly speaking, a Debian question; so I have marked it
off-topic.  But I suspect that it is of interest to users of this list,
since this list is accessed via e-mail.

-- 
  .''`.     Stephen Powell    <zlinuxman@wowway.com>
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