Cómo posponer los correos en Gmail para iOS
Several users have independently detected a change that can affect all those who send mail from an Apple address using external clients . Apparently, a recent change in Apple’s email authentication protocol.
This change means that if you send mail using an @icloud.com, @me.com or @mac.com address from a non-Apple mail client, the mail has a chance to end up in the SPAM folder of the recipient(s). The reason for this has not been fully confirmed, but it is happening.
Why this change? Because Apple may have changed the settings of the DMARC authentication protocol of the emails to a mode called ‘Quarantine’. In that mode, emails are likely to be treated as spam if they are sent from unofficial Apple clients.
In other words, if you’ve configured the Gmail website to send mail from there using an Apple address (or if you’ve done the same thing with clients like Outlook or Thunderbird), check with whoever you’re sending mail to to make sure everything is received properly. To ensure this, the best thing you can do right now is to send those emails with Apple addresses from the official Mail client.
From MacRumors they have also received an alternative that has not yet been verified as working: configuring that external mail client you use to use the address smtp.mail.me.com to send the emails.
The change may be due to an improvement in email security by Apple, so that your addresses are not used to spread phishing or SPAM attacks. We will see if Cupertino offers any explanation.