Please pardon if I have missed the answer to newly failing email sent from phpBB3 v3.1.5.
We now get "535 Incorrect authentication data" even though the phpBB smtp setup is as before and the authentication to email works manually.
Other (lesser?) hostings have suggested that permissions of /home/"username"/etc/ need to be changed to username:mail . Being a mere Spark client here, I have no access to chown -R to see if this cures.
How to restore email functionality to phpBB?

Here's the phpBB error log (sensitive removed):
Email error
» EMAIL/SMTP
/phpBB/memberlist.php

Ran into problems sending email at Line 1479. Response: 535 Incorrect authentication data
.
Backtrace

Connecting to mail.housewheat.com:25
LINE: 1020 <- 220-whub47.webhostinghub.com ESMTP Exim 4.85 #2 Tue, 07 Jul 2015 14:52:59 -0700

LINE: 1020 <- 220-We do not authorize the use of this system to transport unsolicited,

LINE: 1020 <- 220 and/or bulk e-mail.

# EHLO whub47.webhostinghub.com
LINE: 1369 <- 250-whub47.webhostinghub.com Hello whub47.webhostinghub.com [192.249.124.14]

LINE: 1369 <- 250-SIZE 52428800

LINE: 1369 <- 250-8BITMIME

LINE: 1369 <- 250-PIPELINING

LINE: 1369 <- 250-AUTH PLAIN LOGIN

LINE: 1369 <- 250-STARTTLS

LINE: 1369 <- 250 HELP

# STARTTLS
LINE: 1414 <- 220 TLS go ahead

# EHLO whub47.webhostinghub.com
LINE: 1369 <- 250-whub47.webhostinghub.com Hello whub47.webhostinghub.com [192.249.124.14]

LINE: 1369 <- 250-SIZE 52428800

LINE: 1369 <- 250-8BITMIME

LINE: 1369 <- 250-PIPELINING

LINE: 1369 <- 250-AUTH PLAIN LOGIN

LINE: 1369 <- 250 HELP

# AUTH PLAIN
LINE: 1472 <- 334

# Omitting sensitive information
LINE: 1479 <- 535 Incorrect authentication data