aol outbound port intermittently fails (re: forced move from verizon email server to aol)

[ChuckK2]

I started using verizon's email when we initially signed up years ago.  However, I then migrated to gmail since it provided excellant spam email detection, whereas verizon did not.  As part of my migration to using gmail, I setup gmail's outbound server to specify my old verzion email address and a verizon outbound port so that the world still saw my 'verizon' email address on my sent emails.  This
worked perfectly - recipients of my emails saw me as xxx@Verizon.net.   Recently, I chose the "move to aol" option offered by verizon.  I am now forced to use aol email servers,  and have similarly updated my gmail outbound server name and port to 'smtp.aol.com', and port '587' (this is done in my gmail settings).  I find that my outbound email performs normally MOST of the time, but NOT all of the time.  Sometimes I get an email send failure as shown below.  This failure persists for hours.  Later, when I resend the email using the same addresses, it sends just fine.  Is the problem with AOL server name and or port?  The error makes it seem like the 'smtp.aol.com' server  is going down or becoming unresponsive.  Help would be appreciated - never had this issue using real verizon mail servers.   

Final-Recipient: rfc822; xyz@aol.com (email address changed by me)
Action: failed
Status: 5.2.1
Remote-MTA: dns; smtp.aol.com (152.163.0.69, the relay for the domain.)
Diagnostic-Code: smtp; 521 5.2.1 :  Service Temporarily Unavailable.
Last-Attempt-Date: Tue, 21 Mar 2017 12:10:40 -0700 (PDT)

[tns2]

Actually the servers for smtp were changed over a year ago.  Thy just didn't let most people know they had done so.  Possibly this is just what it says, a Temporary outage.  They had an extended outage just the other may

[ChuckK2]

As I indicated in my original forum entry, my problem is happening now (in Mar, Apr 2017), not last year, and only after I chose to migrate my verizon email to aol as requested by verizon.  The outbound aol server is having intermittent problems NOW.  This just happened again today, Mon, 03 Apr 2017 08:28:17 -0700 (PDT) as shown below.  Just cannot get good reliable service these days...

Final-Recipient: rfc822; xyz
Action: failed
Status: 5.2.1
Remote-MTA: dns; smtp.aol.com (64.12.88.133, the relay for the domain.)
Diagnostic-Code: smtp; 521 5.2.1 :  Service Temporarily Unavailable.
Last-Attempt-Date: Mon, 03 Apr 2017 08:28:17 -0700 (PDT)
 

[tns2]

I just noticed a mention of port 587.  Port 465 and ssl were required for verizon, although they may not be for AOL.