Comment by vee-kay

Agreed.

That "Mark as Spam" facility not only moves the offending message into Jink/Spam folder, it also allows the Email Service provider to identify that type of email as spam, so future incoming messages that match that may criteria can be categorized as spam, so they'll go into spam folder automatically, rather than into the Inbox. You can find them in the Jink/Spam folder.

However, if thousands of users report same domain or sender as spam, then the email service provider may take stern action, including blocking the sender email id or domain at the server level, so their messages will never reach your mailbox.

So you need to be careful what you "Report as Spam". It is different action from "Mark as Spam".

"Report as Spam" may also prompt the user to "Block sender", so one must be careful not to block legitimate senders, though this action can usually be undone, as the Mailbox Settings will track the blocked senders so that lost can be corrected by the user if needed.

Gmail has a good trick that most users don't know or notice: In the Spam folder, the user can see a warning at the top of each email that explains why Gmail sent it to Spam.

So user can figure out why legitimate emails got wrongly flagged as Spam, and can prevent such future legitimate emails from falling into Spam folder: User can do this either by adding the sender to Contacts list (Emails from known Contacts are auto-dumped into Spam folder), or by creating a filter to identify and action that message (flag it as Important, or label it with a custom category label, or move it to a specific subfolder, or forward it to another email ID).