Issue Email send problem

[Netgen]

I have one client who try to send email and get that error
<***@gmail.com>: host gmail-smtp-in.l.google.com[***.217.***.27] said:
550-5.7.1 [5.1**.17.*** 12] Our system has detected that this message
is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to
Gmail, 550-5.7.1 this message has been blocked. Please visit 550-5.7.1
Why has Gmail blocked my messages? - Gmail Help 550 5.7.1 for
more information. fj3si6790613ejc.963 - gsmtp (in reply to end of DATA
command)

I have already cloudflare protection, clamv on server and spam protection.
The client also forwarding to an gmail the main emails and now cant send anything!

i have also limit 10 mails send per hour, why happened that?

Also i have these emails in queue Screenshot i tried to insert on spam but still getting messages
is the correct way to block email this : Screenshot or this Screenshot

 

[Thomas Wilhelmi]

A very short research on Google led me to this article: GMail blocks mail

 

[Bitpalast]

The problem normally results from users' habit to forward mail. Mail forwarding seems to be something that users love. Instead of simply using a local mailbox, they forward mail. It almost seems that only a forwarded mail is a good mail. This behavior results in spam being forwarded, too. Everytime a user who has configured mail forwarding, receives a spam, that spam is also forwarded. Recipient mail services such as Yahoo, GMail, Freenet, T-Online, everything from United Internet like GMX, web.de etc. sees such spam and says: "Hey, that server is sending spam to us, let's block it". These providers don't block the actually sender of the spam what they could easily do. They block the forwarder.

The solution is to not forward emails to freemail services, but to use the POP collector services. For example Gmail can collect emails from other mailboxes. In that case it does not matter whether spam is collected. Mails will always safely arrive in the Gmail account.

Sure this is no solution for regular mails being sent to Gmail. But when your server stops sending spam to GMail, sooner or later GMail will remove your ip from their internal "spammer" block list and your server will be able to send mails directly to Gmail accounts again.

 

[Netgen]

The problem normally results from users' habit to forward mail. Mail forwarding seems to be something that users love. Instead of simply using a local mailbox, they forward mail. It almost seems that only a forwarded mail is a good mail. This behavior results in spam being forwarded, too. Everytime a user who has configured mail forwarding, receives a spam, that spam is also forwarded. Recipient mail services such as Yahoo, GMail, Freenet, T-Online, everything from United Internet like GMX, web.de etc. sees such spam and says: "Hey, that server is sending spam to us, let's block it". These providers don't block the actually sender of the spam what they could easily do. They block the forwarder.

The solution is to not forward emails to freemail services, but to use the POP collector services. For example Gmail can collect emails from other mailboxes. In that case it does not matter whether spam is collected. Mails will always safely arrive in the Gmail account.

Sure this is no solution for regular mails being sent to Gmail. But when your server stops sending spam to GMail, sooner or later GMail will remove your ip from their internal "spammer" block list and your server will be able to send mails directly to Gmail accounts again.

So the main problem is the forwarding on Gmail accounts, i already disable the forward to see if everything will be ok.
Can you help me which is the correct way to block an email or a hole domain to avoid receive spams? i describe above

 

[GravuTrad]

The solution is to not forward emails to freemail services, but to use the POP collector services. For example Gmail can collect emails from other mailboxes. In that case it does not matter whether spam is collected. Mails will always safely arrive in the Gmail account.

Could you better explain me how to set this please? thanks

 

[Bitpalast]

Read Gmail messages on other email clients using POP - Gmail Help

You can open your messages from Gmail in other mail clients that support POP, like Microsoft Outlook. Step 1: Make sure POP is the best way to read your emails IMAP and POP are both ways to

support.google.com