Problem sending email - specific domains

Problem sending email - specific domains

Hi,

i'm having issues sending emails to specific domains,

namely:
hotmail.com and  toa-eu.com

 

    ----- The following addresses had fatal errors -----   

   [Status: Error, Address: <xxxx_xxxx@hotmail.com>, ResponseCode 421, 4.7.0 Temporarily Deferred]

 

Message will be retried for 4 more day(s)

 

    ----- Transcript of session follows -----   

 

 Received:from XXXXxxxxxXXXXxxx(xxxxxxxxxxxxxx [xxx.xxx.xx.xxxx]) by mx.zohomail.com

               with SMTPS id 1483521855889565.8622075957446; Wed, 4 Jan 2017 01:24:15 -0800 (PST)  Message-ID:<000601d2666c$54c39290$fe4ab7b0$@avpro.pt>

 Date:Wed, 4 Jan 2017 09:24:18 -0000

and

This message was created automatically by mail delivery system.

 

THIS IS A WARNING MESSAGE ONLY.

 

YOU DO NOT NEED TO RESEND YOUR MESSAGE.

 

The original message was received at Tue, 20 Dec 2016 10:40:48 -0800  from XXXXXX@avpro.pt [xxxxxx@avpro.pt]

 

    ----- The following addresses had fatal errors -----   

   [Status: Error, Address: <xxx1@toa-eu.com>, ResponseCode 421, Read timed out, Status: Error, Address: <xxx2@toa-eu.com>, ResponseCode 421, Read timed out, Status: Error, Address: <xxx3@toa-eu.com>, ResponseCode 421, Read timed out]

 

Message will be retried for 4 more day(s)

 

    ----- Transcript of session follows -----   

 

 Received:from XXXXXXX(bl17-53-83.dsl.telepac.pt [1xx.xx.xxx.xx3]) by mx.zohomail.com

               with SMTPS id 1482255331183840.38382861962; Tue, 20 Dec 2016 09:35:31 -0800 (PST)  Message-ID:<000201d25ae7$76460050$62d200f0$@avpro.pt>

 Date:Tue, 20 Dec 2016 17:35:28 -0000