Question
550 5.4.1 Recipient address rejected:
We can see that xxxxxxx@xxxx record is marked as Email Invalid with cause '550 5.4.1 Recipient address rejected', and unable to send any email from Marketo.
But Salesperson is able to send him email outside of Marketo.
Can anyone please let me know when the 550 5.4.1 error occur and why Salesperson is able to send email outside of Marketo?