Custom domains: sent too many test emails. Possible remedies?

Hi, I'm new to custom domain emails. Recently, I followed the instructions of easydmarc.com's email deliverability test and sent test emails to a large number of recipients. Now, I got errors from mailbox.org's Mail Delivery System, informing me that

<ed-global@centrum.cz>: host centrum-cz-10mx1.eco-mx.cz[46.255.225.8] said: 554
    Your access to this mail system has been rejected due to poor reputation of
    a domain used in message transfer (in reply to MAIL FROM command)

host mx.yandex.ru[2a02:6b8::311] said: 554 5.7.1
    Message rejected under suspicion of SPAM; https://ya.cc/1IrBc
    1786951812-AUOni61YMiE0-oIo2luCo (in reply to end of DATA command)

Gmail has detected an unusual rate of mail originating
    from your SPF <redacted> domain [<redacted?      35]. To protect our users
    from spam, mail sent <redacted> from your domain has been temporarily rate
    limited.